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.

^^ 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