holy shit dudes did you know there's a black hole at the center of the milky way?

i don't know why i always thought the sun was the center of the milky way. boy was i rong! it's a supermassive black hole referred to as sagitarius A
http://news.nationalgeographic.com/news/2005/11/1102_051102_black_hole.html
does this mean that eventually our entire solar system will be compressed into a 'singularity' perhaps like in a billion years or some shit.

yes

Haha knew this was a jdchurchill thread w/o even looking.

http://www.environmentalgraffiti.com/sciencetech/supermassive-black-hole-milky-way/6671

also spelled sagittarrius A* rong

There's a supermassive black hole in the center of every spiral galaxy.

You're nothing special.

b-but EARTH is SPECIAL

http://en.wikipedia.org/wiki/Sagittarius_A*

becuz i live here

As for the solar system, the Earth, and the descendents of yourself and everyone you know; our star has orbited the galactic center about 50 times in the 4.6 million years since it coalesced out of dust from a past supernova. In all likelyhood, it will orbit the galactic center another 40 times before our star becomes a red giant and engulfs our planet it its hot atmosphere.

You and your descendants needn't worry about it. Main sequence stars like our own gradually increase radiation output as they age, and current estimates are that Earth only has about 800 to 1000 million years before insolation boils off all water on the surface. If your descendants haven't migrated off world by then, well, nice try, guys.

http://www.sai.msu.su/apod/image/0012/SgrA_sharp.gif

ayo!

http://www.astro.ucla.edu/~ghezgroup/gc/images/2008orbits_animfull.gif

i don't know why i always thought the sun was the center of the milky way.

:O

sum1 needs a map of the milky way shower curtain

was waiting for caek tbh

http://www.dailymail.co.uk/home/moslive/article-1269288/STEPHEN-HAWKING-How-build-time-machine.html

waiting for icp's response

"I know you were hopin' for something more satirical but we honestly believe that black holes are miracles"
-- ICP

http://upload.wikimedia.org/wikipedia/commons/a/a0/16-cell.gif

http://upload.wikimedia.org/wikipedia/commons/f/f4/24-cell.gif

http://a1star.com/images/wildstars.gif

yo caek wtf is that gif?

i'll concede that i'm a knucklehead about the sun being the center of the galaxy. but really how many of us wrap our minds around this? i mean i and my classmates built little mobiles with styrofoam and hangers in grade school and then i never really thought about it much after that.

http://www.clipboom.com/public/galleria/Astronomy/000981.gif

but this stephen hawking dude really blows my mind, man

i thought the center of the milky way was caramel and nougat

lolz

sum1 needs a map of the milky way shower curtain

― Baedeker's time and space (Lamp), Tuesday, May 4, 2010 2:06 PM (21 minutes ago)

dude they don't manufacture these, do they?

yo sanpaku: what planet/galaxy are you from?

ayo jdchurchill, I work for an astronomy journal, ask me anything

You can find me here:

http://ipac.jpl.nasa.gov/media_images/sig05-010.jpg

so every galaxy has a black hole at the center? my gurl ask me "what's a black hole?" and i said it was like a drain and that's what got me thinking cuz many galaxies have this spiral shape just like water going down a drain

dan m: what's up wit all dat radiation that come outta black holes?

like in this jpg
http://msnbcmedia4.msn.com/i/msnbc/Components/Photo/_new/080903-space-blackhole-bcol-11a.jpg

man, I have no idea

http://en.wikipedia.org/wiki/Hawking_radiation

Pretty sure it is like a drain and eventually all matter will get sucked in, yet time relative to a life of a human on planet earth this will take FOREVER and is going in SUPER SLOW MOTION. If you were to be in a stable orbit in/very near the black hole it would all be happening pretty fast.

Black holes are simply ordinary mass concentrated enough that the escape velocity exceeds that of light.

Earth's escape velocity: 11.2 km/s
Our sun's escape velocity (from the surface): 617.5 km/s
Minimum escape velocity for a black hole: 299,792 km/s

In our era, most black holes arise because of supermassive stars collapsing. In galactic centers, there's been plenty of time for the carcasses of supermassive stars to fall in their accidental way into the event horizon (simply the lightspeed orbit) of past carcasses.

But, random density variations could produce black holes dating to the big bang. Over long periods, black holes are believed to evaporate due to Hawking radiation (AFAIK, this is Stephen Hawking's main contribution to astrophysics). So, any black hole that survived since the BB would have had to be considerably larger. Moreover, Hawking radiation means that in the long term, all mass isn't absorbed into black holes, but instead is dispersed, and the long term fate of the universe is a high-entropy luke-warm cloud with very little in the way of pop-stars and sex objects.

Hawking radiation, the layman's explanation:

Empty space, if you could look closely enough, is a cauldron of particle pairs appearing and disappearing spontaneously. While it seems absurd at the macro scale, conservation laws have another interpretation at the quantum level, and universal accountancy takes effect on the macro level.

This spontaneous creation distruction also occurs at the event horizon, or sphere at the lightspeed escape velocity radius, of black holes. Sometimes, one of the particles in a pair is sucked in (to never be seen again) into the event horizon, while the other escapes.

Through Hawking radiation, the universe corrects this accounting error. The black hole loses mass to counter the radiated particle.

Physics is cool. I wish I'd had the sense for math to pursue it further.

"Black holes are simply ordinary mass concentrated enough that the escape velocity exceeds that of light."

ok sanpaku: why is they 'concentrating' so much?

and then like in the explanation of other elements besides hydrogen why they 'concentrating' so hard they fusion?

My understanding: they concentrate by Newtonian gravity and friction. Without velocity being lost through the bump and grind of particle hitting particle, asteroid hitting asteroid, planet hitting planet, and star hitting star, all matter would just orbit, relatively uninvolved, forever.

But, when velocity is lost through chance meetings and slow viscous raport, things slow down. Attraction prevails.

It's very sexual.

As for thermonuclear fusion, most of it happens like this:

Imagine a hot, crowded party with a lot of Hydrogen, like in the center of most stars.

Two meet briefly, but can only join into a deuterium (H2) nucleus if they release excess charge and spin as an positron and electron neutrino. Those neutrinos fly off without effecting much, like the bass frequencies at a club, the positron is totally embarassed to be seen in this purely matter affair and finds an electron (the opposite sex) to grind with, and they explode in dancefloor lust into pure light and heat.

Deuterium nucleus is a strange but enticing creature, and finds another lonely Hydrogen nucleus to bump into, and their union is light Helium, making more light and heat.

Light Helium is still more promiscuous, and can either dance with another light helium (making regular Helium, 2 more light Helium, and some light), or can dance with regular Helium (making Berylium, light, heat, and sexual frisson).

It's very sexual.

― nori dusted (Sanpaku), Tuesday, May 4, 2010 9:40 PM (17 minutes ago) Bookmark Suggest Ban Permalink

using this as the epigraph for my thesis if that's ok

http://www.bathsheba.com/crystal/galaxy/galaxy_movie.gifhttp://www.bathsheba.com/crystal/galaxy/galaxy_movie.gifhttp://www.bathsheba.com/crystal/galaxy/galaxy_movie.gif

"If you were to be in a stable orbit in/very near the black hole it would all be happening pretty fast."

huh. that hawking time travel article linked above says time slows down at the black hole cuz 'mass drags on time'

or did you mean like the radius is smaller so the orbits happen faster?

also if the hydrogen is just 'concentrating' by gravity why don't we have any stars on earth? we have hydrogen and gravity . . .

To break the dancefloor analogies, my understanding of galactic spiral arms (and caek can correct me on this, s/he's WAY more qualified) is that the spiral arms of galaxies occur because not because matter is spiralling into a black-hole drain at the center, but simply because while everything is orbiting the galactic center of mass, they also have gravitational effects on other orbiting things. The arms occur quite naturally from the mutual attraction within neighborhoods of matter orbiting around the center of mass. The arms don't have a permanent population, gas and stars sometimes are part of them, and sometimes are thrown before or behind them in orbit, but on average, stars and matter spend more time within arms than outside them.

Perhaps Caek can tell us why globular clusters don't exhibit spiral patterns. Is it because they are old, and interstellar gas has all become part of stellar systems and isn't really visible? Is it because they don't have a predominant orbital plane, so lots of material is orbiting the gravitational center but doesn't resolve (from our observational vantage) into clear spiral arms? I'm curious. And mostly sexual.

I love this but at the same time...
http://www.ludditemachine.org/blog/uploaded_images/head_explode-779507.jpg

caek all tight lipped . . .

"If you were to be in a stable orbit in/very near the black hole it would all be happening pretty fast."

huh. that hawking time travel article linked above says time slows down at the black hole cuz 'mass drags on time'

The theory is that, since time is going slow at the black hole, and since you are there, time is going slow for you, yet for the rest of the universe time is going fast. In fact, faster and faster the closer you get into the black hole, relative to you. What feels like seconds to you is weeks or months to someone outside of a black hole.

This is from one essay I read by Hawking where he theorized that if you could fall into a black hole and remain looking backwards at the rest of the universe, you would see the entire remainder of time happen faster and faster. At least until you were torn to pieces.

Perhaps Caek can tell us why globular clusters don't exhibit spiral patterns. Is it because they are old, and interstellar gas has all become part of stellar systems and isn't really visible?

I'm going with because they are old, and the tendency I see of things to 'smooth out' and become less easily defined over time in a fluid or otherwise dynamic system. What if over time the brighter and more luminescent stars that would be forming a spiral go supernova and thus have less defined shapes?

Sanpaku, you're my favorite poster these days. Feel free to school us on this stuff as much as you'd like!

i have to go to bed here. by the time i wake up i fully expect sanpaku to have figured out time and space. if he fails then i will try to explain spiral arms. they are v. important for the evolution of disk galaxies.

"for beginners"
http://www.astro.ucla.edu/~ghezgroup/gc/journey/

http://www.astro.ucla.edu/~ghezgroup/gc/journey/images/genzel2.jpg

http://upload.wikimedia.org/wikipedia/en/6/68/Swans_-_Great_Annihilator.jpg

sum1 needs a map of the milky way shower curtain

― Baedeker's time and space (Lamp), Tuesday, May 4, 2010 2:06 PM (21 minutes ago)

hmm you would have to have a pretty big shower

^thought abt writing that and decided not to

yeah but you could design it so that the 'black hole' fits right over your shower 'drain'!!

One of the neatest things about these galactic center black holes is that its theoretically possible to orbit within their event horizon.

Gravity falls with the square of distance. Your feet are attracted to the center of the Earth more than your head.

For larger masses, this tidal effect grows. For example, Jupiter's moon Io would be too small to have tectonic events like volcanism if it orbited at a much greater distance. But as the closest orbiting Galilean satellite, the tidal effects are enough to pull the moon into an egg shape and churn and heat the interior. Its volcanic spumes of brightly colored sulfur compounds arise as a result.

For "normal", star mass black holes, tidal effects near the event horizon are huge. Were you to approach or orbit one in a standing position, your feet would experience so much greater gravity than your head that you would be pulled apart, and your constituent parts would be drawn into a thin strand. Astronomers, being otherworldly erudite nerds, have found an equally erudite term for the condition: Spaghettification.

For a supermassive black hole, like the one in the center of our galaxy which masses 4.1 million Suns, has an event horizon so distant from the singularity that tidal effects are much smaller. Space farers can theoretically approach and orbit just under the event horizon at light speed (and consequent not-quite infinite time dilation), surviving their exit from the visible universe. Time dilation effects there are so great that provided they weren't obliterated by other matter entering at light-speed, they could survive much of the time till the the end of the visible universe outside.

If you could find an isolated supermassive black hole unlikely to grow from further collisions, it would make an ideal time capsule. Sometime in the distant future, even galactic center black holes will evaporate through Hawking radiation, and your parcel will emerge into a sparse vacumn occupied only by widely separated supermassive black holes and diffuse, near absolute zero background radiation.

Young Sanpaku:

http://torp.priv.no/woody/images/annie-02.jpg

caek, are you ever going to contribute to this conversation which so befits you?
(in the limited understanding i have of you)

god this thread brings up just as many questions as answers . . .

oh hi! sorry, the election + the riddles of the universe intervened.

so the deal with spiral arms is, that they can only form (or they can only be observed) in flat, disky systems of stars and gas. globular clusters don't fit the bill because they are round and contain no gas (because they are the oldest systems of stars, and all the gas fuel has been converted into stars). the disk has to be "cold" (in the sense that the gas isn't jiggling about too much), as well as flat (although the two kind of go hand in hand).

they are "density waves", which means they are perturbations that pass through the medium (which is stars and gas in this case), rather than a wave of the medium itself. this is kind of like waves in the mid-ocean: the waves passes through the medium, an individual drop of water moves up and down as it passes through, but is not actually part of the wave moving left and right. (this analogy breaks down at beaches, where water itself is actually pushed up the beach). but anyway, these density waves pass through the medium of stars and gas, and the result in shock waves and compression of gas. compression or (relatively) cold gas like this results in the formation of stars. these bursts of knotty star formation make the spiral density waves readily visible -- they look like a string of pearls. this is the whirlpool galaxy:

http://imgsrc.hubblesite.org/hu/db/images/hs-2001-10-a-large_web.jpg

any non-axisymmetric feature in a galaxy (e.g. spiral arms or bars) can drive material inward or outwards. in the absence of such a feature it's actually incredibly difficult to get stars off the kinds of stable near-circular orbits we have in the solar system or even off highly eccentric plunging orbits like comets (this is why we can predict the arrival of periodic comets with ludicrous accuracy -- we know nothing happens to them that could affect their orbit even while we can't see them).

galaxy scale spiral arms are responsible for some interesting stuff, but in the context of the supermassive black hole (SMBH) in the centre of each galaxy, the important thing is the accretion disk. this is a very small disk of mostly gas around the black hole that feeds it. like any disk of gas, even though this is many thousand times smaller than the galaxy, this probably has spiral arms (although i don't think these small spiral arms have been directly observed). here's an impression of an accretion disk around an SMBH:

http://www.sciencecentric.com/images/news/black_hole_art_612_400.jpg

as sanpaku says, gas is "dissipative" this means that it exerts friction on itself. this allows it to get rid of energy (in the form of radio emission, i.e. an "active galactic nucleus") and fall off its circular orbit into the black hole, fuelling its growth. if you can't get rid of your orbital energy, you can't get rid of the orbit you're on. stars presumably do fall into black holes very occasionally, but it's quite difficult to get this to happen because of conservation of angular momentum in non-dissipative systems, and they are not a significant source of fuel.

the growing black hole is interesting in itself (but not something i know much about -- general relativity is wicked hard). more important for the stuff i do is that, despite the fact that the black hole is ~1/1000th of the mass of the galaxy, the extreme radiation released by the gas just before it falls in is thought to be on of the things that regulating the growth of the entire galaxy on the macro scale. this is a nearby galaxy called Cen A (it's not a disk, hence no galaxy-scale spiral arms). it's a great example of a massive outflow of energy from the nucleus. it's easy to see by looking at it that that outflow from the nucleus is going to affect the growth and evolution of the galaxy.

http://www.mpe.mpg.de/~hcs/Cen-A/Pictures/apex-cen-a-m.jpg

the stars you can pick out as individual twinkles in that cen a image are foreground stars in the milky way. cen a is the white cloud (you can't see its individual stars in this image).

thanks for this.

though i admit this is the kind of stuff that keeps me up nights.

more important for the stuff i do

What is the stuff you do? Thanks 4 the awesome info!

i am finishing a phd in disk galaxy evolution. some of my stuff is on graphspergers - the graphs and quantitative visualization thread and ♪♫ caek's corner ♪♫.

gd space is p fukken rad looken

http://stsciopo.cachefly.net/hu/db/images/hs-2007-16-a-xlarge_web.jpg

^^^ best

http://stsciopo.cachefly.net/hu/db/images/hs-2007-16-a-xlarge_web.jpg

^^^ best

^^^ best

― caek, Sunday, May 9, 2010 3:29 PM (57 seconds ago) Bookmark Suggest Ban Permalink

^^^ best

― caek, Sunday, May 9, 2010 3:29 PM (1 minute ago) Bookmark Suggest Ban Permalink

ILX wormhole

lol

fuck causality imo

http://www.astro.ucla.edu/~ghezgroup/gc/images/2008orbits_animfull.gif

yo caek wtf is that gif?

it's stars in the centre of the galaxy. most stars move too slowly given their distance for the change in their position to be apparent on the timescale of a human lifetime/PhD project. one place where that isn't true in the MW is at the centre of the MW, where we know there there is a massive, invisible concentration of mass, i.e. a black hole thanks to these observations. you add up all the mass you can see, you set a simulation running in a computer, and the simulation doesn't orbit like the observations unless you stick a invisible thing that is 1,000,000x the mass of the sun at the place they (confusingly) mark with a star.

MW = milky way

here's all the SMBH whose masses we have been able to determine directly from the motions of stars around them. (you can also estimate their mass indirectly from the energy in the outlows, but that involves making assumptions we haven't yet verified, whereas these depend on well-understood newtonian mechanics.)

http://img208.imageshack.us/img208/8423/picture2es.png

the y-axis here is in units of the mass of our sun. "10^6" is a 1 with six zeros, i.e. 1 million, "10^9" = 1 billion.

the x axis is a measure of the speed with which stars are orbiting the center of the galaxy.

things to note:

the milky way is near the bottom and labelled "MW". it has a relatively small black hole. it's "only" 1,000,000 solar masses, whereas most other measurements are more like 1 billion. this is mostly due to the fact that this plot is incomplete: its difficult to determine the mass "small" black holes unless they happen to be nearby, like the centre of the MW, so they are missing from the plot. it's like fishing with a net: most of the fish you catch are bigger than the holes in the net. this does not prove there are no small fish.

the line is a fit to all the data. as you can see there is a clear correlation between the mass of the black hole and the speed with which stars rotate. the speed this stars rotate is mostly determined by the mass of the galaxy though. you could replace the x-axis with galaxy mass and the correlation would be just as tight. this suggests that there is actually a correlation between black hole mass and host galaxy mass. this is a major result in galaxy evolution. it's one of the reasons we think this tiny black holes (tiny both in terms of size and mass compared to the galaxy) are so important in regulating galaxy evolution. if the growth of the black hole and the galaxy weren't closely related, why would their masses be so tightly correlated?

note astronomers have pretty low standards for what they call a "tight correlation" compared to the rest of physics.

I wanna just show these images to everyone who ever said science is killing god or taking the mystery out of life. I say if your work involves cosmic visions it must be at times very spiritually fulfilling!

space is magical

http://i50.photobucket.com/albums/f325/caek/clip_image002.jpg

Looking at awesome space pictures and reading caek's amazing explanations always reminds me of this pic, which in it's quiet way, freaks my brain.
http://www.nasa.gov/centers/jpl/images/content/161974main_pia00452-browse.jpg

remind me, what's the dot again?

pretty, Ned. what is it though?

http://en.wikipedia.org/wiki/Pale_Blue_Dot

But don't forget the camera adds 10 pounds.

yeesh

so how accurate a representation of a black hole is the disney film of the same name? like 80% accurate? 75%?

by the way astrophysics is responsible for some of the most poetic and suggestive phrases and concepts ever. my favorite is "event horizon." what a beautiful phrase.

it is 80% accurate

guys i've actually not looked at this thread but it's like all of my favrit things and now i can't wait to go home and ignore my gf to read it so thks from me

"event horizon." what a beautiful phrase.

shit movie though

this looks pretty accurate

http://www.jrinla.com/movie-reviews/black-hole-screenshots/black-hole28.jpg

it does

it's like a black hole in that u can't even see it

caek do u get to fuck with huge telescopes a bunch or is it more working with simulations

first three years of my phd was all simulations, but this year i am fucking with pretty big telescopes.

in january i used the 200" (~5m) on mount palomar, which was amazing. it's a beautiful cathedral-like old school telescope and because of the optics the dome is much bigger than it would be on a modern 4m telescope. here's its mirror arriving in pasadena in 1936.

http://www.astro.caltech.edu/palomar/images/blog/E-50sm.jpg

it's still very much a world class telescope, although its proximity to LA and the ocean causes problems with light pollution and image quality. we were using the laser to do adaptive optics. we fire a laser beam into the sky, it reflects of a layer of sodium in the atmosphere at ~80km to create a simulated star. the mirror of the telescope is deformed v. rapidly to make the "star" look like a point rather than a twinkle, which sharpens the image of the galaxy we're looking at. here's an example of what the laser it does when you look at the moon:

http://www.astro.caltech.edu/palomar/images/blog/LCROSS.gif

we were actually the last people to use the laser on palomar, probably for ever. it's spectacularly dangerous to use it near airports, which palomar is. you need radar and four "spotters" who are people who have to stand outside all night looking for planes. you also have to phone "space command", which is some NSA thing, before you turn the laser on. they sometimes say "no", but never say why. the assumption is spy satellites. if you put your telescope in the desert in chile you don't have to worry about this stuff, which is incredibly expensive.

next month i am going to the mcdonald observatory in near marfa in west texas for a long (9 night) observing run. the telescope we're using famously has bullet holes in the mirror from where a technician had a breakdown and shot it. (lol texas.)

http://www.everyjoe.com/files/191/2007/06/mirrorholes.jpg

i have never been to chile, but i work for ESO, which runs the european telescopes in the southern hemisphere. we have 4 8m "Very Large" telescopes down there, and a handful of smaller (2m and 4m) telescopes.
eso is going to build the E-ELT (european extremely large telescope), which will have a 42m (!) mirror.

http://www.sciencenews.org/pictures/052309/feat_neweyes_e-elt_zoom.jpg

the biggest telescopes in the world are the two 10m Keck telescopes on Mauna Kea in hawaii. they belong to caltech and UC.

http://www.ifa.hawaii.edu/users/cowie/z6/kecks.jpg

and also this unusual binocular telescope in arizona, which as 2x8m mirrors with an effective collecting power of a 12m mirror.

http://www.popsci.com/files/imagecache/bown_article_image/articles/binocular-telescope.jpg

rubbish post imo.

you think you're so clever with ur phd in astrophysics.

well HOW COME YOU'RE NOT ON TV THEN EH?

~rad~

42m fuuuck

i am on imdb fwiw

link

yeah i fuckin thought so. astrophysicists are lyin mfers ime

My visit to Mt Palomar - A blog

Here is a fucking bobcat by the residence, which is about 1/4 mile from the 200" telescope

http://img219.imageshack.us/img219/390/img3295hz.jpg

You can drive that 1/4 mile if you want, but if you do then you are a fool because you miss out on sights like this:

http://img709.imageshack.us/img709/8967/img3303da.jpg

and this view of the old 60" telescope at twilight. this is the telescope edwin hubble used.

http://img706.imageshack.us/img706/7886/img3309a.jpg

this is what it looks like as you approach the 200" in the afternoon (you usually go up around 4pm to check everything is ok)

http://img697.imageshack.us/img697/3788/img3327d.jpg

and then you go back to the residence for dinner and then go up again at twilight

http://img526.imageshack.us/img526/9062/img3318g.jpg

this is what it looks like if you drive. it's big!

http://img413.imageshack.us/img413/5473/img3305k.jpg

this is me on my way back to the residence on my last afternoon

http://img28.imageshack.us/img28/6581/img3341g.jpg

i love mount palomar. it is so pretty it makes me barf. if you are in southern cal. you should visit! they take you on a tour of the 200" and you can buy avocados and gamble in the indian casino on the way.

so damned jealous tbh

same

"Astronomers are reporting that they have detected the most distant cluster of galaxies ever seen: a mind-smashing 9.6 billion light years away, 400 million light years more distant than the previous record holder. The cluster, handily named SXDF-XCLJ0218-0510, was seen in infrared images by the giant Subaru telescope, and confirmed with spectroscopy and the X-ray detection of million-degree gas (a smoking gun of clusters). Every time astronomers push back the record for clusters, they learn more about the early conditions of the Universe, so this cluster will provide insight into how the Universe itself changed over the first few billion years after the Big Bang."

http://science.slashdot.org/story/10/05/10/1617255/Record-Breaking-Galaxy-Cluster-Found?from=rss&utm_source=feedburner&utm_medium=feed&utm_campaign=Feed:+Slashdot/slashdot+(Slashdot)

Amazing photos btw! Count me as one of the jealous..

That binocular telescope seems like it would be perfect for 3D imaging for close up objects....possibly? Maybe they are too close together and you would ideally just use one telescope with photos taken at different times in the Earth's orbit.

Do you know anything about cosmic 3dimensional imagery? It seems like it would be of alot of help w determining distances and making more accurate measurements.

you can't do 3d imaging of objects at these kind of distances. the "pupils" would have to be separated by a distance much greater than the size of the solar system. the binocular thing is a good way of improving "collecting power" (i.e. how long you need to look at a patch of sky to collect enough photons for your image to be more than just noise) without having to deal with the engineering difficulties of building a bigger mirror.

you can do something called "interferometry" to reconstruct images taken with multiple radio telescopes, e.g. the very large array in NM

http://upload.wikimedia.org/wikipedia/commons/6/63/USA.NM.VeryLargeArray.02.jpg

interferometry is mathematically extremely complicated and i don't understand it, but what you get for all that maths is improved spatial resolution (you can pick out more detail in a given amount of time), rather than more collecting power (you can see fainter objects in a given amount of time).

coming in 2014: WEBB

http://webbtelescope.org/webb_telescope/science_on_the_edge/graphics/sci-stars-carina-big.jpg

i am shocked that you can just shoot a telescope twice and not completely ruin it!

as long as it doesn't shatter, it's fine. you can put a black piece of paper on a big mirror like that and all it does is reduce the collecting power.

The full precipitating causes may never be known, but one February night in 1970 a McDonald Observatory employee (not a Texan, but an Ohioan newly hired from another observatory!) suffered a breakdown and carried a pistol to the observing floor of the 107-inch telescope. He fired a shot at his supervisor, and then unloaded the rest of the clip into the primary mirror. Happily, fused silica is more resilent than ordinary glass, and the big mirror did not break. The craters have been bored out and painted black to reduce any light-scattering effect, and the end result is simply a slight reduction in the efficiency of the telescope. It is now the equivalent of a 106-inch telescope. The incident made the national television news, with Walter Cronkite describing it before a projection showing the wrong telescope upside down.

"as sanpaku says, gas is "dissipative" this means that it exerts friction on itself. this allows it to get rid of energy (in the form of radio emission, i.e. an "active galactic nucleus") and fall off its circular orbit into the black hole, fuelling its growth."

this means radioactivity? what emission? and yr talking about hydrogen here, right? also on the very pretty pictures those are not something you can "see" as in photons, are they? they have to do false color of like what . . . i guess i am asking how astronomers are representing these things. like stars i get it's light, so we are looking at a normal photograph. but i am sure that there are other emissions that we can collect but i would like someone to explain them to me, please.

also talk to me about some dark matter. i saw this program last night called how the universe works the episode entitled 'alien galaxies' wherein they referenced ziwiki(sp) the dude who came up with the concept of dark matter. and as in any pop science piece the nitty gritty details were glossed over but i don't understand how we infer it's existence. they said something about gravitational lensing which they used an analogy of the fishbowl and how it distorts an image . . .

http://upload.wikimedia.org/wikipedia/commons/e/e0/EnsteinRingZoomOptimised.gif

still to hear an explanation of 'dark matter' that doesn't smack of 'our maths aren't working, let dark matter = x'

you do, of course, have to put that through a filter of these people being an awful lot smarter than me, of course.

http://en.wikipedia.org/wiki/Dark_matter
http://en.wikipedia.org/wiki/Big_Bang

For example, hydrogen atoms emit radio waves of wavelength 21.12 cm. oh ok

from the dark matter wiki

The first person to provide evidence and infer the presence of dark matter was Swiss astrophysicist Fritz Zwicky, of the California Institute of Technology in 1933.[6] He applied the virial theorem to the Coma cluster of galaxies and obtained evidence of unseen mass. Zwicky estimated the cluster's total mass based on the motions of galaxies near its edge and compared that estimate to one based on the number of galaxies and total brightness of the cluster. He found that there was about 400 times more estimated mass than was visually observable. The gravity of the visible galaxies in the cluster would be far too small for such fast orbits, so something extra was required. This is known as the "missing mass problem". Based on these conclusions, Zwicky inferred that there must be some non-visible form of matter which would provide enough of the mass and gravity to hold the cluster together.

http://upload.wikimedia.org/wikipedia/commons/0/02/Gravitational_lens-full.jpg

big space arrows

hey caek, i've been to mt. palomar a couple times - grew up in san diego, went there for field trips in elementary school twice, and then a few other times to go sledding and stuff in the winter. it is indeed very nice, though i never saw any bobcats.

this means radioactivity? what emission? and yr talking about hydrogen here, right? also on the very pretty pictures those are not something you can "see" as in photons, are they? they have to do false color of like what . . . i guess i am asking how astronomers are representing these things. like stars i get it's light, so we are looking at a normal photograph. but i am sure that there are other emissions that we can collect but i would like someone to explain them to me, please.

"radioactivity" is usually used to mean atoms breaking apart releasing protons/neutrons or gamma rays (which are high energy photons). that kind of process is one way of getting "radiation", but not what i'm talking about here. the gas heats up and when it does it releases the energy in the form of photons. these are mostly at radio-type frequencies (hot 97FM), but there are visible at optical wavelengths (i.e. w/ your eyes if you have amazing eyesight/an optical telescope). and when these jets of radiation get outside the host galaxy they encounter more diffuse gas and release x-rays.

that picture of Cen A is a composite of a radio and optical and x-ray image, so yes, it's false colour. the best way to learn about a galaxy is to look at it at lots of wavelengths. you can see the kinds of different structure doing this reveals on the Cen A wikipedia page: http://en.wikipedia.org/wiki/Centaurus_A.

optical light is collected with a normal telescope. radio with one of those big dishes like in jodie foster's contact with matthew mcconaughey (or an array of those). x-ray is absorbed by the atmosphere, so you have to have a space telescope (or at least a high altitude balloon) to detect that.

http://upload.wikimedia.org/wikipedia/commons/thumb/e/ee/Ill-2_O3.jpg/800px-Ill-2_O3.jpg

also talk to me about some dark matter. i saw this program last night called how the universe works the episode entitled 'alien galaxies' wherein they referenced ziwiki(sp) the dude who came up with the concept of dark matter. and as in any pop science piece the nitty gritty details were glossed over but i don't understand how we infer it's existence. they said something about gravitational lensing which they used an analogy of the fishbowl and how it distorts an image . . .

yeah, lensing is one way. there are a bunch of ways of figuring out how much mass must be in a patch of sky, sometimes from how the stars move (that's what i do), or by gravitational lensing (mass bends light, and if you measure the amount of bend you can figure out the amount of mass). you take one of these estimates of how much mass there is, and you compare it to how much stars and gas you can see, and they don't agree, so we know either (i) our understanding of gravity on astronomical scales is wrong or (ii) there is some mass we can't see, i.e. "dark matter".

if (ii) then this dark matter stuff must be very weakly interacting. it doesn't reflect light. doesn't participate in nuclear processes. etc. all it does is exert a gravitational pull. this makes it very difficult to directly detect. people are trying though, and there have been claims of detections in literally the last few months. difficult to know how that will play out.

Gravitational lensing is cool. The distorted and magnified blue disk galaxy images are all of the same galaxy, some is 10 billion light years away, while galaxy cluster 0024+1654 in the center (the gravitational lens) is about 5 billion light years distant.

http://www.math.sunysb.edu/~tony/whatsnew/column/grav-lens-0299/images/HSTgravlens.jpg

One can work backwards from the observed bending of light to the mass distribution responsible, which is one way the relative amonts of ordinary and dark matter has been determined:

http://www.physics.monash.edu.au/assets/images/cl0024+1654.jpg

how 'bout this: caek do you believe zwicky and vera rubin?

so wait dark matter is basically something that registers as a kind of void--we can't measure it directly, and don't understand what it consists of, but we know it exists based on best working models of astrophysical phenomena?

eeeeeeee love this thread!

how 'bout this: caek do you believe zwicky and vera rubin?

― a fool committed to a VISION of SOMETHING NO ONE ELSE UNDERSTANDS (jdchurchill), Tuesday, May 11, 2010 8:38 PM (35 minutes ago) Bookmark Suggest Ban Permalink

i've met vera rubin. she's great. total empiricist. all you can ever get her to say is that her sums don't add up, and this is by how much.

so wait dark matter is basically something that registers as a kind of void--we can't measure it directly, and don't understand what it consists of, but we know it exists based on best working models of astrophysical phenomena?

― by another name (amateurist), Tuesday, May 11, 2010 8:47 PM (26 minutes ago) Bookmark Suggest Ban Permalink

we can measure it's gravitational pull because there is so much of it, but we can't directly detect the particles it is presumably made up of (yet).

dark matter, assuming it exists, is like 80% of the mass in the universe btw.

on that program i mentioned above they elaborated on how galaxies should basicly fly apart but they don't and this is due to the dark matter "holding" them together. can you refer me to some such literature about this? and also they went on about how the dark matter puts galaxies into clusters and the clusters into superstructures which is about where my mind exploded. they 'zoomed out' from milky way into these superstructures and it looked like a spider web type matrix or maybe filamentary structures in a cell.

they visited a place where these dudes amplify laser beams like a million times so that they can shoot it at a little pinhead thing and try to model when the stars explode as they die or whatever, and a place where they try to recreate the hydrogen fusing into helium in like this big magnetized bottle the dude called it. anyone who is interested in this thread should likely check into this program i saw it on discovery channel, yo.

this thread sort of makes me want to drop out of life and study astrophysics.

given that i flunked college physics, it'd be a long haul.

^^ haha I was just thinking what I would need to do in order to pull a complete 180 and start studying astrophysics. never took a hard science course in college ;_;

by literature do you mean scientific papers or pop science books? everyone should read "our cosmic habitat" by martin rees. that is the best pop astronomy book imo. the canonical references from the scientific literature for rotation curves and high mass-to-light ratios are probably Faber and Gallagher (1979) and van Albada and Sancisi (1986) (click the PDF links to read the paper, although i'm not 100% sure they will work if you're not on a university network).

the basic idea is the following: if you're orbiting something like the sun, the speed you go round and round gets lower as you get further away. this is because its gravitational pull goes down, so the speed you need to whizz round it to prevent yourself falling in is lower. we can see this works by looking at the planets. the earth is going round the sun at
about 30 km/s, but neptune is only doing 5 km/s. the formula is velocity = square root of (G * mass of sun / distance to sun). G is the gravitational constant, and this is "newtonian gravity".

but with galaxies (and clusters of galaxies) there is a problem. the vast majority of their visible mass is in stars. but there's a small amount of gas outside the stars that allows you to measure the orbital speed (or "circular velocity") at radii beyond the stars. because we can't see much mass out there, we expect this gas to be orbiting more slowly than gas within the galaxy. that's not what happens:

http://img72.imageshack.us/img72/4472/picture2rb.png

ignore the lines for now. the points are observations. the stars (i.e. the visible mass) extends to a radius of about 6 kpc (a kiloparsec is about 3000 light years), but you can see that gas is orbiting at 150km/s way, way beyond the edge of the galaxy. given how much mass we can see, this makes no sense. the gravitational pull of the visible galaxy isn't strong enough to hold gas in an orbit at that speed. this is like whizzing a slingshot round too fast to hold.

the (preferred) explanation is that there is mass we can't see in the form of a halo dark matter that extends beyond the galaxy, and supports high circular velocities beyond the visible galaxy.

the line on that plot labelled "disk" is how fast we expect the gas to be orbiting, given how much mass we can see. it underpredicts the observations, especially beyond ~6 kpc.

the discrepancy is sometimes quantified as a mass-to-light ratio, M/L. we infer mass within a radius from the circular velocity (remember the formula, so the mass within a given radius = v^2 * distance from center of galaxy /G). We then measure the amount of light within that radius. We write the mass in units of the mass of the sun (e.g. 1 billion solar masses), and the light in units of the luminosity of the sun (e.g. 100 million solar luminosities). the M/L is that case is 1 billion/100 million = 10. the fact that it is significantly bigger than the expected value of 1 is one of the sources of evidence for dark matter.

an alternative explanation is that, at least on galactic scales, newtonian gravity is wrong. there is no extra dark mass. the problem is the formula we're using to turn velocity into mass is wrong. i say "on galactic scales" because newtonian mechanics has been verified to preposterous accuracies on smaller scales. this idea is known as "modified newtonian dynamics". it is a very interesting possibility, but i think it raises more questions than it solves, so most people are comfortable with the idea of dark matter (which also solves a lot of other problems, not just rotation curves).

and also they went on about how the dark matter puts galaxies into clusters and the clusters into superstructures which is about where my mind exploded. they 'zoomed out' from milky way into these superstructures and it looked like a spider web type matrix or maybe filamentary structures in a cell.

yeah, this is the basic picture of how galaxies formed. after the big bang you've got this fairly (but not perfectly) smooth mass distribution, where the mass is 80% dark, and 20% hydrogen and helium gas. over time, gravity starts to turn the random fluctuations in the initial conditions into bigger and bigger clumps or gas and dark matter. there's a huge amount of uncertainty about the order things happened, etc. but these clumps are now visible as galaxies.

remember the gas is dissipative. that means it can get rid of energy and fall into the middle of things. upthread it was falling into black holes, but here it's falling into the "dark halos". eventually it reaches sufficient density to form stars, and you get a galaxy in the middle of the halo. dark matter is not dissipative, so it stays kind of "puffed up" bigger than the galaxy at its center. so rather than discrete balls of dark matter, you get this sort of cosmic web.

that's the idea anyway, and it's consistent with a lot of observations, but observing this process directly is obviously pretty difficult. the pictures they showed on that tv show were probably from something like the millennium simulation, which put a bunch of gas and dark matter in a computer program and let it run fast forward for 15 billion years to see what happened. they got galaxies rather like we see in the real world, so the assumption is they are on the right track.

http://upload.wikimedia.org/wikipedia/commons/thumb/5/58/AstroMSseqF_063aL_%2818135101%29.jpg/800px-AstroMSseqF_063aL_%2818135101%29.jpg

all those yellow dots are galaxies. purple is dark matter (which is of course invisible in the real world, assuming it exists). there are problems with this picture (you get far too many small galaxies, the galaxies don't look much like the milky way, etc.). these are probably due to our lack of understanding of gas physics rather than dark matter. dark matter is actually very simple. you've just got to worry about gravity. gas does all sorts of ridiculously complicated stuff we don't understand, and even if we did understand it, which we don't, it does stuff on scales that are too small to be resolved in simulations with present computers. and then you've got the feedback from the black holes i was talking about, which is obviously not easy to simulate.

btw i have a book at home written by brian may from queen & patrick moore called 'BANG' and it's p awesome too.

may be a little light fro what caek's driving at but i suspect that it might be more the appropriate level for those of us dipping our toes into the galaxy.

pretty videos of structure formation:

http://cosmicweb.uchicago.edu/
http://www.mpa-garching.mpg.de/galform/virgo/millennium/

i haven't read it, but i've heard nothing but good things about the bill bryson book too!

not strictly limited to astrophysics but bryson book is A++++ required reading for everyone that's interested in stuff.

so apparently this things can get quite rowdy

http://news.bbc.co.uk/1/hi/science_and_environment/10108226.stm

struggling to make a joke with 'barred spiral'

gas does all sorts of ridiculously complicated stuff we don't understand, and even if we did understand it, which we don't, it does stuff on scales that are too small to be resolved in simulations with present computers

Makes me think of fluid dynamics and my personal favorite pop science book "Chaos: Making a New Science" by James Gleick!

so in that millenium simulation picture above it shows a line of scale that is 31.25 megaparsecs per hour? wtf?

also just like thanks and wow caek you are really inspiring alot of minds here, dude
this stuff is fascinating!

gonna read those papers you linked to above over the next weeks (printed 'em!) and hopefully score that cosmic habitat in the library as soon as i finish this murakami book i'm stuck on.

No, h there is a constant. It represents our uncertainty about the Hubble constant, which is capital H. H = (100 km/s/Mpc) / h. So if h = 1, H = 100. Most evidence points to h = about 0.7, i.e. H = 70.

The Hubble constant sets the scale of cosmological simulations. Presenting them like this, e.g. 31.25 Mpc/h, means that if we find out h = 0.5 or something, we don't have to throw out the simulations.

H (or h) is one of the most uncertain measurements in physics, given how important it is. Best estimates have varied by a factor of about 2 or 3 since it was first defined.

It measures the acceleration of the universe. A galaxy 1 Mpc away from us is receeding from us with a velocity of about 70 km/s. This is due to the expansion of the universe. A galaxy 100 Mpc at about 7000km/s. You have to make observations on many scales to pin it down though, because in addition to that expansion of the universe, there's random motions and gravitational interactions. E.g. one of our nearest giant spiral galaxy neighbour, Andromeda, is moving towards us at over 100km/s, and will merge/pass through/collide with the Milky Way in about 5bn years.

oh ok. it's like a normalizing thing. b/c the hubble is out there and do we know how fast it's going? but it's also like surfing on the expansion of the universe too, eh? how the fuck are we ever going to know what big H is?

well, they're narrowing down. The year 7 results from WMAP (the microwave satellite) say its between 69.0 and 71.7 km/s/Mpc.

ime we need a jerry bruckheimer movie about galaxies colliding.

the weird thing is, at least as far as stars and planets are concerned, it's unlikely to make that much difference. you can see why from the following fun fact: if you packed wasps into an area as densely as stars in the milky way, there would be seven wasps in the whole of europe. throw two of those at each other and there's very unlikely to be any direct collisions. the average gravitational field changes, but not in a way that would affect life. and stars don't collide with other stars. also, the collision takes billions of years.

well that's why we need jerry bruckheimer and not you tbh

ps seven wasps in europe is too many. all wasps are bastards.

true x 2

"Stars are born in a region of high density Nebula, and condenses into a huge globule of gas and dust and contracts under its own gravity."

why does it contract under it's own gravity? and is hydrogen the only thing that does this?

I always get the feeling there's something ridiculously simple staring us in the face about all this stuff about time and matter and energy and gravity and singularity and space and speed and we just can't put 2 & 2 together.

time slows down near mass
+
singularities are infinitely massive
+
black holes suck up mass
+
photons have no mass
+
space and time expand at the speed of light
+
the singularity at the start of the big bang was infinitely massive too
+
...

= something or other that we missed and explains everything! E.g. time only feels like it's moving forward for us non-infinitely massive bits inside the singularity because we're shrinking at the speed of light and the black holes we see sucking up mass are feeding the singularity we're in! Hooray! Please send nobel prize to my mail address. kthxbye.

I stared at the sky when stoned once and came to the same conclusion. We're onto something, you and I.

like it's some giant child under a black sheet making all this happen

http://en.wikipedia.org/wiki/Stellar_evolution
http://en.wikipedia.org/wiki/Giant_molecular_cloud

http://www.msnbc.msn.com/id/37259986/ns/technology_and_science-space/?gt1=43001

Isn't it amazing how we can know all this stuff about something (in this case 600) light years away? But at the same time we kill each other over drawings of prophets and other imaginary friend crap, let companies destroy seas and hide their crimes because money is more important, etc etc etc?

in fact, some people would even get killed for the phrasing "drawings of prophets and other imaginary friend crap"

I always get the feeling there's something ridiculously simple staring us in the face about all this stuff about time and matter and energy and gravity and singularity and space and speed and we just can't put 2 & 2 together.

time slows down near mass
+
singularities are infinitely massive
+
black holes suck up mass
+
photons have no mass
+
space and time expand at the speed of light
+
the singularity at the start of the big bang was infinitely massive too
+
...

= something or other that we missed and explains everything! E.g. time only feels like it's moving forward for us non-infinitely massive bits inside the singularity because we're shrinking at the speed of light and the black holes we see sucking up mass are feeding the singularity we're in! Hooray! Please send nobel prize to my mail address. kthxbye.

― StanM, Thursday, May 13, 2010 3:04 PM (1 week ago) Bookmark Suggest Ban Permalink

I have been pondering this exact thing this year (and sake recently helped a dinner table rant that surely was unwelcomed).

StanM, don't fool yrself holmes: that same money that corporations are hiding behind is what funds the telescopes that get pointed at the planet being absorbed into that star and the scientists operating it. except that the money is from the guvermint.

oh no guys - astrology is socializm!
run!

http://bradleymonton.files.wordpress.com/2008/09/mandelbrot.jpg

^ freaks me out just as much as crazy galaxy shit, tbh. worlds within worlds for ever and ever.

microcosm vs macrocosm

http://upload.wikimedia.org/wikipedia/en/c/ce/Mandelbrot_zoom.gif

nothing to say, but bumping b/c this thread is fascinating.

inspiring and depressing in equal measure

so i just looked up what those mandelbrot things are... mind: blown.

he's a policy advisor to labour uk?

No, that's his son.

if we could just fukkin figure out quantum mechanics . . .

Easy! Unfortunately, hanc marginis exiguitas non caperet.

"I have uncovered a wonderful proof. Unfortunately Hank Marvin is too small to contain it."

'Cubum autem in duos cubos, aut quadratoquadratum in duos quadratoquadratos, et generaliter nullam in infinitum ultra quadratum potestatem in duos eiusdem nominis fas est dividere: cuius rei demonstrationem mirabilem sane detexi. Hanc marginis exiguitas non caperet.

'It is impossible for a cube to be written as a sum of two cubes or a fourth power to be written as the sum of two fourth powers or, in general, for any number which is a power greater than the second to be written as a sum of two like powers. I have a truly marvellous demonstration of this proposition which this margin is too narrow to contain.

For the next three hundred and twenty-five years mathematicians tried and failed to reconstruct the 'marvellous' proof which Fermat had teasingly withheld. Fermat's Last Theorem, as it became known, was eventually proved in 1995 under extraordinary circumstances by the English mathematician Andrew Wiles. The proof cost him six years of solitary effort to achieve, and runs to well over a hundred pages. In the course of proving FLT, Wiles also managed to go a long way towards proving a much more important result, the Taniyama-Shimura Conjecture, which concerns a deep link between two otherwise unrelated areas of mathematics.

^not sure how this connects with the discussion tho

Not at all. It was just a way to weasel out of having to try to understand quantum mechanics. "I totally understand, but this here text box is too small to explain. Too bad, eh? Bye!"

I don't know if Fermat really had a proof, I'm using his trick. :-)

Guys Fermat's Last Theorem was a Dan Brown teaser, rd yr blgs

here's a page on atomic absorption and emission spectra that can help explain some of the images we see of stars etc such as today's APOD

http://csep10.phys.utk.edu/astr162/lect/light/absorption.html

http://antwrp.gsfc.nasa.gov/diamond_jubilee/debate96.html

and like whoa dude is there north south east west (and then what)
north south east west is only x and y we need a z axis here
how do they navigate in space?

also how do they take these wonderful images i see of like galaxies and what-not when the earth is spinning on it's axis and around the sun thus changing the 3d orientation in regard to photographed object . . .

oh i guess it won't be that hard to navigate