Sharpest ever view of the Andromeda Galaxy (2015) | Hacker News Reader

Sharpest ever view of the Andromeda Galaxy (2015)

spacetelescope.org

274 pointsdavid9097 comments

Two things are amazing (to me) about this picture.

1) When you look up in the sky at the Andromeda Galaxy, your retina is absorbing photons that have been screaming through space for 2.5 million years. If you were on the Earth then, you'd be hanging out with Smilodon, the saber-toothed cat. For 2.5 million years, those photons were freely zooming through space and time, and when you see them, those photons are gone forever, their energy powering a chemical reaction in the rods and cones lining your retina that enables you to see them. Those ancient photons were seen by nobody else but you, and they literally become a part of you.

2) In about 3.75 billion years, the Andromeda Galaxy, currently zipping through space toward the Milky Way Galaxy at 110 km/s (nearly 70 miles per second, or about 250,000 MPH), will collide with and merge with our galactic home. It's unlikely anything would happen to the majority of planetary systems in either galaxy (there's a lot of empty space in there) -- but the night sky (not from Earth, we'd probably be cooked by the Sun by then) sure would be beautiful. And bright.

Scientists even proposed the name for the new galaxy: Milkomeda.

I was thinking a similiar thing last night when I read this news. What we observed through the Hubble telescope now about the Andromeda Galaxy happened 2.5 millions years ago. What is it actually doing right now? Is it still alive?

On an astrological scale isn't 2.5 million years a very, very short period of time?

Yes. Our own galactic 'year' is 250 million years (the time it takes to rotate in place once). So 2.5 million years is about a galactic day (or maybe a weekend).

Wow, I feel so small, physically and temporally!

I wonder if this proposal will be remembered by our successors and their counterparties when the time comes.

> For 2.5 million years, those photons were freely zooming through space [...]

Imagine the faces of Penzias and Wilson when they learned that the noise in their horn antenna wasn't bird poop but photons traveling 14 billion years without interacting.

See Cosmic Microwave Background.

I wish there was a night sky render of that.

Sometimes I sit outside with one of the sky/star apps and look for stars that are about the same light years away as I am old. It's neat to think about the light leaving that star when I was born and taking my entire life to reach me. The scale of the universe and our place in it is hard to fully comprehend.

Especially on #2. The sheer size of the galaxy is so mind-boggling. So many stars, and each one could potentially have some form of life on a planet around it. And it's just one galaxy of billions (or is it trillions? I forget, but it's already so huge that it hardly matters). So far away that we can hardly conceive of the idea of ever going there. But wait, it's already coming to us! More quickly than any realistic form of propulsion we could come up with.

Fun NDG quote regarding #1. It's 2.5 million years from our frame of reference, but an instant for the photon.

> Photons have no ticking time at all, which means, as far as they are concerned, they are absorbed the instant they are emitted, even if the distance traveled is across the universe itself.

No way saber toothed cats could pronounce "S"!

Question about #1: Where did the photons originate though? Did the Andromeda Galaxy create its own, or were these bounced off and we see (basically) the reflection?

The photons almost all originated in stars in the Andromeda Galaxy. A very small number reflected off of gas in the interstellar medium, but nothing your eye could detect.

> the night sky (not from Earth, we'd probably be cooked by the Sun by then) sure would be beautiful. And bright

Brighter, yes, but not very bright. The density of stars will not increase very much. Currently, to see the Milky Way, you have to be out in the boondocks, far from cities and other light polluters - the thing is just so faint.

After the merger, perhaps it will get brighter, but the increase will not be spectacular. The brightness of the combined galaxy as seen from Earth will be dictated by the stellar density, which will not change much.

>your retina is absorbing photons that have been screaming through space for 2.5 million years

according to QM idea of superposition collapse that photon has just decided to collapse in your retina while it had non-zero probability of collapsing into retina of an alien anywhere on that 2.5 million radius circle. That blows my imagination :)

This is the imagery released in January 2015. Though not brand new, this is an amazing image to contemplate, especially in light of the continued discoveries from Kepler.

Edit: Don't miss the link in the article to the slippy map zoomable version at https://www.spacetelescope.org/images/heic1502a/zoomable/

Sorry if this is a dumb question (the article pretty much says it): when you zoom all of the way in, each dot is a star (or cluster of stars)?

Not really, but close. Picture is 1.5 billion pixels and features 100 million stars. So it’s about one star per fifteen pixels.

100 billion stars, not million. So on the order of 100 stars per pixel, although obviously not evenly distributed.

(Edited to add) The individual stars you can see when you zoom all the way in are the very brightest stars, mostly blue (O/B class) or red (K/M class) giants. For each star you can see, there are hundreds of smaller stars that you can't make out individually but contribute to the general background glow.

> 100 billion stars, not million

No, it's 100 million, as the article says.

> It is the biggest Hubble image ever released and shows over 100 million stars and thousands of star clusters embedded in a section of the galaxy’s pancake-shaped disc stretching across over 40 000 light-years.

I think maybe the op meant the entire Andromeda galaxy is estimated to have 200-400 billion stars (source Wikipedia)

Actually, Wikipedia says the number of stars is estimated at 10^12 (a trillion).

(And whoever guesses the closest gets the whole jar!)

> For each star you can see, there are hundreds of smaller stars that you can't make out individually but contribute to the general background glow.

Yeah, like ours.

Yes, or close! Zoom in right near the top right edge, should help clear that up for you :)

How does that really clear anything up? (Not being snarky, just wondering what you mean)? That the space between stars/clusters become a little more apparent?

http://imgur.com/XSgigtY

The bright parts are boring, let's look at the empty ones! http://petapixel.com/2013/06/06/a-mind-bending-look-at-the-h...

Now while watching the video, do keep that picture of Andromeda in the back of your mind, and that the Hubble telescope was aimed at the darkest corner of the universe! Factor in Kepler stuff, and draw your own conclusions.

And zooming back, here I am, sitting on a chair in an irrelevant part of that thin blue layer on a ball of iron and oxygen, crying of joy, hope, and a little bit of sadness for those of us that keep throwing flak – whether bombs or words – at each other in a delusion of self-importance. How feeble are we, merely able to be at peace with our kin; how frail, when we can barely camp out in such close proximity to our home. Please, world, let's race to space again, in a – this time around – friendly competition.

Very profound. Thank you for sharing.

There is a very big bright object in the middle of the image a bit to the bottom. You can't miss it. Do you have an idea what it is? It is the brightest object visible on the image apart from the galactic core.

It's a foreground star in our galaxy.

I'm having a hard time understanding this picture along with what I understand of the scale of space. The Andromeda Galaxy is big, and it has a lot of stars. Which is to say, it's REALLY big, and it merely has a bunch of stars, so the size of the stars should be very small compared to the empty space between the stars, even if you are looking through the galaxy. I would assume that if you get a better and better image, you'll be seeing the holes better just like you'll see the stars better. Kind of a fractal effect: when you look closer, you see the same kind of density but at different scales.

But if I zoom into this image it just feels like I'm seeing a mush of speckled light. What's up with that? How much of the image is an artifact of the telescope?

Not an astronomer, but I'll give it a shot.

If you do the zoom thing, at the highest level? Yes, it's a mush of speckled light -- looks a lot like a noisy or grainy RGB image.

But what I think you're seeing are the actual stars -- thousands or maybe ten thousands of them in a full screen at the highest zoom. They're all clumped together because you're looking cross-wise at the galaxy, through the disc. So there so many stars at the highest level of zoom that the image looks grainy.

As a somewhat astronomer, this explanation seems reasonable.

Usually you can't discern individual stars in another galaxy, like in the center of the Andromeda galaxy (But doing statistics is still possible). However, the Andromeda galaxy seems close enough that at the outer edge of it, you can isolate them to do astronomy on individual stars (like spectroscopy).

Edit: Also, you can find stars in almost all colors. The average of the colors depends on the age of the stars in the galaxy. If there are only a few new stars born, the galaxy will appear redder. If there are many new stars born, it appears bluer (see Hertzsprung-Russel diagram). The way the stars appear in different colors means that they have different ages and masses.

Noise in a telescope (except for high energy particles hitting your detector) is thermal noise. It will only appear if there's almost no light detected. So if it were noise, it should be the other way round: Noisy where there are little stars and no noise where there are a lot of stars. If you'd ask me, I'd say there's exactly zero visible noise in there.

As a former astronomer, this is correct. Even in extremely high resolution images each pixel contains many, many stars. This fact has actually been used to determine the distances to galaxies. The basic idea is that if the galaxy is nearby, then there will be fewer stars per pixel (say, only a few dozen), but if the galaxy is very far away, there will be many thousands of stars per pixel. As a result, if the galaxy is nearby, there will be a lot of variation in brightness from pixel to pixel because the Poisson fluctuations are proportionally much larger. If the galaxy is more distant, the brightness at each pixel will be more homogenous. This is called the surface brightness fluctuation technique.

There's a nice page about it here: https://ned.ipac.caltech.edu/level5/Jacoby/Jacoby9_1.html

A couple things to keep in mind:

Andromeda is so big that to see it, you're looking through a large portion of the Milky Way. Some of the really bright looking stars in this picture are actually in the Milky Way.

There is a ton of space between stars, but they're also not completely flat. It's less like a sheet of paper and more like a thick pancake.

So-called "empty" space isn't empty. Some of it is mostly just a vacuum, but lots of empty space is filled with gas which is glowing due to latent light/heat/radiation. In that regard, parts of this picture are glowing similarly to shining a flashlight in fog.

Even if you managed to zoom in close enough to an empty spot between stars in our galaxy, which also was an empty spot between the stars and gas in Andromeda, you would still start seeing the distant galaxies far beyond Andromeda. The Hubble Deep Field [1] is a good demonstration of this effect. They pointed the Hubble at a previously thought "empty" region of space and held it there for about 10 days. After gathering all the received photons collected over that time into a single image they realized that even "empty" space is full of a lot of stuff if you look far enough out.

[1] https://en.wikipedia.org/wiki/Hubble_Deep_Field

those specks are not noise, they are stars! if you zoom in to the darkest top right corner, you'll see that there's in fact no noise in the image.

On that note, the stars all have a 'stellation' along what appear to be the same axes. What is this effect? On the surface of the Earth my assumption was that the stellation/twinkling is an atmospheric thing. In this case is it an effect of gases or some telescopic thing?

Actually if it were telescopic it could probably be analyzed out.

In telescope photos it's often caused by diffraction off the 'spider' that holds optical elements in the centre of the telescope's barrel.

I was wondering why every star showed a pair of perpendicular lines radiating out. Apparently they are artifacts of the telescope's construction, and are called "diffraction spikes" [1].

[1]: https://en.wikipedia.org/wiki/Diffraction_spike

There is a nice Minute Earth video about this, for those who want a quick and entertaining way to get the concept: https://www.youtube.com/watch?v=VVAKFJ8VVp4

It recently struck me, that if Andromeda would be visible to the naked eye, it would be huge on the night sky:

http://sploid.gizmodo.com/the-incredibly-huge-size-of-androm...

It is visible to the naked eye. It looks more like a cloud and doesn't have as large of an apparent diameter though.

I think the center is faintly visible. Doubt you can make out the whole thing.

Correct. Only the core is visible to the naked eye, and even then you'd have to be out in the boondocks, far from cities and other light polluters.

I've had this image downloaded at full res for over a year now, and I love to project this at actual size onto my wall (with some good, mysterious mood music). Makes a really neat effect and is fascinating to look at once you realize what you're gazing upon. It's even a good conversation starter. (I'm fun at parties...)

Just scrolling the image around in Preview makes my Mac slow to a crawl.

Preview fails me surprisingly often. Can't even PDF properly. Try something else.

(I'm fun at parties too)

"...I love to project this at actual size onto my wall ..."

you have a 40,000 light year wall in your house?

I meant that the image is not zoomed out and it pans across the width and height of the image on the wall. ;)

If you like this you might also enjoy this [1] 46 billion pixel image of our own galaxy (sadly not as sharp as the andromeda one). Taken from a link [2] I posted a while back.

[1] http://gds.astro.rub.de/

[2] http://aktuell.ruhr-uni-bochum.de/pm2015/pm00143.html.en

I've enjoyed this video exploration of the image:

Gigapixels of Andromeda: https://www.youtube.com/watch?v=udAL48P5NJU

Beautiful. Whenever I see images like this of "big things" in space I'm reminded how meaningless our short existence on this little rock is from a universal perspective. My big takeaway is always to try to find personal meaning in ones life. Either in work, or family, hobbies, etc.

It's taken 15 billion years since the big bang for our relatively complex atoms to form - from supernovae. Yes, we were generated in the core of stars. The entire superstructure of the universe is what allows us to exist in the first place.

This is an ignorant question, but when you zoom in full, is every light dot a star? Or is it noise, like you get with a poorly lighted photo?

They are all stars as far as I know

At 100% zoom you will see that they have different sizes. Noise has usually the same size (the size of one pixel on the sensor, if not using bayer filtering).

Then you take a look at the XDF[1], showing ~5500 galaxies like this one in a tiny angular diameter, and you realize how big the Universe is.

[1] http://hubblesite.org/newscenter/archive/releases/2012/37/im...

It's cool hey! That image covers the same area as approximately four full moons, 2.3 arcminutes by 2 arcminutes. [1]

So, back of the envelope calculation multiplying 5500 by the area of the full sky (as though the earth were invisible) we get ~242 billion galaxies, which is close to what this[2] claims at 100 to 200 billion galaxies.

Space is big.

1. https://en.wikipedia.org/wiki/Hubble_eXtreme_Deep_Field

2. http://www.space.com/25303-how-many-galaxies-are-in-the-univ...

The moon is about 30 arcminutes across (half a degree) [0], which is considerably larger than the area of the Extreme Deep Field. But the estimate of the number of galaxies is okay.

The Hubble Ultra-Deep Field (of which the Extreme Deep Field is a part) is one thirteen-millionth part of the full sky. [1]

The full sky is about 41,253 square degrees in size. [2]

I think the HXDF is one 32-millionth of the full sky. If so, multiplying 32 million by the 5500 galaxies in the XDF gives on the order of 200 billion galaxies, as you said.

[0] https://en.wikipedia.org/wiki/Angular_diameter

[1] https://en.wikipedia.org/wiki/Hubble_Ultra-Deep_Field

[2] https://en.wikipedia.org/wiki/Square_degree

Yes, you're right, thanks for the correction: the Extreme Deep Field image is smaller than the moon. I neglected to click on the image at [1], thereby missing the detail in the full size image[2].

1. https://en.wikipedia.org/wiki/Hubble_eXtreme_Deep_Field 2. https://en.wikipedia.org/wiki/Hubble_eXtreme_Deep_Field#/med...

I'd imagine some of the really bright ones are either galaxies in the background or milky way stars in the foreground. No idea though.

Using the zoom tool recommended in the article really provides perspective. Especially when you see those stars clustered close together when each of them are really millions of miles apart (aside from the binaries) with possible planets orbiting them. Now consider the billions of galaxies out there. I'm positive there's an Alien or two there as well.

You're off by an order of magnitude.

Stars are often trillions of miles apart. Binaries can be so close they touch or as far apart as 100 billion miles.

As for the aliens, there are good arguments for and against their existence. The numerical argument is not, by itself, very convincing. It's like thinking you will win the lotto because you have a million tickets, but not knowing how many balls are drawn and how many numbers are on the balls. You may be guaranteed to win, or your odds may be effectively zero.

I suppose my mistake made it an order of magnitude more amazing!

Link to full resolution downloads: http://hubblesite.org/gallery/album/galaxy/pr2015002a/titles...

Original size: A mere 4.3 GB.

Another really great picture taken by Hubble is the eXtreme Deep Field. As wiki puts it: Except for a few stars, every speck of light is an entire galaxy – some of these are as old as 13.2 billion years

https://en.wikipedia.org/wiki/Hubble_eXtreme_Deep_Field

I occasionally use that image as my desktop. It reminds me of how insignificant we really are.

I'm not an astronomer as evidenced by this question:

What's the bright glowing light that's partially cropped in the lower left of the image? Is that a large star cluster? Or a single star? Or something else?

Yes it's a large cluster of stars. At the very center of the galaxy you will also find a supermassive black hole.

Is there a name for that super massive black hole? (serious question) Just curious to learn more.

I don't believe they've ever named it; it is indeed "supermassive" (around 2.3 billion of our suns).

The supermassive black hole at the center of the Milky Way is called Sagittarius A* ("Sagittarius A-Star"), the only named supermassive black hole I could find in any reports.

For context, see https://www.spacetelescope.org/images/heic1502c/

the image is lovely. the zoom tool is missing a feature to link at specific places - like, there's a galaxy visible trough the background at a certain place, but you cannot share it

also it's surprisingly detailed and noisy, where usually it's an either or. It makes me suspect the noise it's actual stuff absorbing/emitting radiation, but I have no idea what's the interference to be expected from dust or if those dots and speckles are all actual stars - anyone has a link with some explanation of what we're looking at?

I'm gonna go out on a limb and say "pancake-shaped disk" is not only redundant (because all disks are pancake-shaped) but backwards (since actually it's pancakes that are disk-shaped - pancakes are a special case of disks, which are really cylinders).

Sorry, this is more fun for me than marveling at the photo. It is pretty cool though.

Does anyone know why those patterns [1] appear when you zoom in like 10 steps or so? Are those stitches or some artifacts of the sensor?

[1] http://www.spacetelescope.org/images/heic1502a/zoomable/

Not sure what patterns you're referring to. Also not sure how big a "step" is - zooming is continuous for me. Might check other browsers (I'm using Chrome)? Or link a screenshot?

I guess he refers to clicking the + button ten times. I'm using Chrome for Android myself.

He may be referring to that, but there doesn't seem to be a per-click zoom amount. It zooms further the longer you hold a click and seems very sensitive.

My god, it's full of stars!

This is extremely cool. I remember going to the observatory as a kid and looking at Andromeda through the telescopes. It's amazing to think we will be one with that galaxy someday, millions of years from now

"the full image [...] has 1.5 billion pixels. You would need more than 600 HD television screens to display the whole image."

True, but not accurate ?

1'500'000'000 / (1980 * 1024) ≈ 739.8 :)

That should be:

1'500'000'000 / (1920 * 1080) ≈ 723.38

Anyway, as you wouldn't want to crop the image you're showing, a more suitable formula would be:

N = ceil(image width / 1920) * ceil(image height / 1080)

Edit: width = 69536, height = 22230 so N = 37*21 = 777

I'd love to see this done with ~200 4k screens ...

Wait? That's not digital noise? Those are actual stars?

It's interesting how uniform Andromeda is. Not much in the way of arms.

Also I'm impressed with the resolution available, you can really zoom in an incredible amount.

It would be nice if they could filter out the intervening objects that are in our own galaxy, to give a clearer perspective.

Fun fact: Andromeda is the only object outside of the local Milky Way group that can be seen with the naked eye.

Not even supernovae?

Should have clarified with permanent object and I'm wrong anyway... Triangulum is visible to the naked eye and further away.

M33 in Triangulum is comfortably visible with the naked eye from dark skies. A few other galaxies have been claimed to have been spotted with the naked eye, although I've never been able to see any of these.

Also, the 'local group' actually includes M31 and M33 in addition to our galaxy and many smaller ones.

You are right. Should have fact checked that before posting.

What do you mean by "local Milky Way group"? The "Local group" is a group of galaxies, containing the MW and Andromeda as its most massive members. The MW plus its satellites isn't called the local Milky Way Group.

What is so bright on the left side -- what looks like the center of the galaxy?

A lot of stars cluster around the supermassive black holes in the center of every galaxy. Also, depending on the area of the spectrum they were examining, a lof X-rays are found there too.

Hmm, expanding zoom tool across three 4k monitors crashes chrome.

They sadly don't have background pics for 4K screens.

is there anything of statistical or other cosmological analytics merit here or is this just for enjoyment?

mind well and truly blown

Reply on news.ycombinator.com