Largest Hubble Mosaics Ever Assembled

bobtheowl2 writes "The Hubble Heritage team of astronomers, who assemble many of the NASA Hubble Space Telescope's most stunning pictures, is celebrating its five-year anniversary with the release of the picturesque Sombrero galaxy. One of the largest Hubble mosaics ever assembled, this magnificent galaxy is nearly one-fifth the diameter of the full moon. The team used Hubble's Advanced Camera for Surveys to take six pictures of the galaxy and then stitched them together to create the final composite image. The photo reveals a swarm of stars in a pancake-shaped disk as well as a glowing central halo of stars."

Comments

Brave, brave people.

[daeley]

Very brave of them to make a 211 MB TIFF file available for download on this page. ;)

Re:Brave, brave people.

[MImeKillEr]

At that size, makes you wonder if its to scale!

Re:Brave, brave people.

[Acidic_Diarrhea]

Ha Ha! You're silly. Of course it is to scale. I think what you mean is that you're wondering if it is to a 1-1 scale because as long as there is a correlation between the real world distances and the distances in the assembled work, there's a scale. So, no - it's not to a 1-1 scale. High resolution photographs, such as the ones that can be produced using Hubble, are pretty big - although, not that big. I bet there's a great compression scheme just waiting to happen on these photos though - lots and lots of black space.

Re:Brave, brave people.

[m00by]

yeah, there's this really cool new compression scheme called jpeg. it takes almost all the data from the 211Mb tiff, and slaps it down in a 7Mb jpg file. wow. just freakin' wow. =D I believe the sarcasm was implied, but hey, just to let you know...it's there. =D

Re:Brave, brave people.

[IM6100]

Yes. It's sort of like mp3. They compress the hell out of the thing so the 'rubes' who just want something kinda pretty can download it faster.

Re:Brave, brave people.

[Bushcat]

That image is well worth panning through: the sheer number of galaxies in the background is astonishing. I guess it's a big place, after all.

Aye, Cap'n!

[rudy_wayne]

At Warp 9 we'll be there in 38,000 years!

700km?

[crow]

this magnificent galaxy is nearly one-fifth the diameter of the full moon

So the galaxy is less than 700km in diameter? Those must be the smallest stars ever discovered.

(Yes, I know that they mean the mosaic covers a region of space that, as observed from earth, covers about one-fifth the diameter of the moon, but they could have worded it better.)

Re:700km?

[PD]

Their wording is actually a very common way for astronomers to describe how big something is. Usually people will say that something is N degrees in size, or X arc-seconds in size, but sometimes they will make reference to the diameter of the moon.

It might not be the most precise and lawyerly language, but in the conventions of astronomical jargon it's unambiguous.

Re:700km?

[Anonymous Coward]

Isn't this only confusing if you're not from earth. :-)

Re:700km?

[antianonymousguestou]

As I'm not an 'active' member any astronomers' circle, I'm still a bit confused as to what they're trying to say when they say that its 1/5 the diameter of the moon. Are they saying that the image produced by Hubble is 1/5 the size of the moon? But what magnification was Hubble operating under to produce that picture? It just seems like they're comparing apples and oranges since one body (the moon) is tangible, where as the other (the picture) is digital. Maybe you can help set me straight.

a 400 mile wide galaxy?

[AtariAmarok]

"this magnificent galaxy is nearly one-fifth the diameter of the full moon."

The moon's diameter is 2140 miles. This equates to a galaxy less than 450 miles wide. How many stars can you fit into such a Minnesota-sized galaxy? How can you make it small enough to be accidentally swallowed by a small dog?

Re:a 400 mile wide galaxy?

[Acidic_Diarrhea]

Chief, if you were to look into the sky, the region of space they have documented covers the same amount of space as the amount of space covered by the moon's diameter. They do not mean that that is the actual size of the galaxy. Do you need a hug?

Re:a 400 mile wide galaxy?

[AtariAmarok]

"Objects in Hubble mirror screen might be closer than they appear to be"

Men in Black

[Anonymous Coward]

They carried galaxies around in key-fobs.

Hey neat

[nocomment]

There's also some nice video footage

It's a photoshop job.

[Peter T Ermit]

There's a number of stars in the foreground that are missing -- presumably, they prettied up the disk a bit to make it more photogenic. (Compare to this ESO shot and you'll see what I mean.) I'm always disappointed when NASA has to bend the truth -- even just a little bit.

(I posted this on metafilter, but it bears a mention on slashdot.)

Re:It's a photoshop job.

[Gogo Dodo]

Okay, I compared them and they look the same to me. I don't see any large differences like missing stars. At least not obvious ones. You do realize that those two photos were taken with two different telescopes, right?

Re:It's a photoshop job.

[Peter T Ermit]

There are a number of missing stars -- look more carefully at the disk. There's a bright one on the left and a smattering on the right. And yes, I realize that ESO is not HST.

Re:It's a photoshop job.

[LMCBoy]

First of all, I don't see any stars in the ESO image that do not appear in the HST image, so what are you talking about?

Maybe you mean that the stars in the ESO image look more prominent than they do in the HST image. That's because the VLT is on the ground, so the stars (which are very pointlike in the HST image) are slightly blurred.

Re:It's a photoshop job.

[Peter T Ermit]

With 6:00 as the point nearest us and 12:00 as the point diametrically opposed through the galactic nucleus--there's a bright one at 7:30, lower part of the dust disk. There's also a bunch on the top of the disk, between 2:00 and 5:00. (And they're all foreground stars, so they're not really associated with the disk).

If you compare the other stars in the image, it's pretty clear that it's not a resolution artifact.

Re:It's a photoshop job.

[Gogo Dodo]

Okay, I looked again. I take it you mean the bright star on the left on the dust lane just a little past where the disk color turns from white to brown. Then two more to the left a little high and a little low. Well, they're there in the HST images, too.

They're not there in the HST "screen" image, but the size is a lot smaller than the ESO image so that's expected.

In the small HST "print" image, which is closer to the size of the ESO image, they are visible, but fainter.

If you switch to the large HST "print" image, they are clearly visible.

Re:It's a photoshop job.

[LMCBoy]

Peter,

I am not usually this relentless, but as an employee at STScI, your accusation of fraud really annoys me.

Anyway, I am prepared to prove you wrong. Please examine the animated GIF image I have placed at the following URL:
http://www.stsci.edu/~jharris/sombrero.gif

In the image, I have stacked the HST image and the VLT image on top of each other, and I am displaying each with the same scale and orientation. The first frame shows the HST image, the second frame shows the VLT image. You may need to set your browser to "loop" animated GIFs, or save it to disk and use a tool like gifview.

The rotation and scale are not perfectly matched, but it's good enough to see correspondence between the images.

Oh, wait. I think I see what you are on about. The "missing" stars are all in the dusty disk, right? If you look closely, they aren't gone in the HST image, just much fainter. The reason is simple: the intervening dust absorbs blue light much more than red light. These disappearing-objects are not foreground stars, they are probably star clusters in the galaxy.

If you read the technical data about each image:
ESO, HST, you'll see that the ESO image was taken through redder filters than the HST image (V,R,I compared to B,V,R), so it's no suprise that the ESO image is going to see through dust better!

Re:It's a photoshop job.

[Peter T Ermit]

Your explanation makes sense; I couldn't see the alternate explanation for the selective dimming -- and now that there is one, I retract my accusation. (Moderators, please mod root post down.)

Re:It's a photoshop job.

[Anonymous Coward]

Thank you for the excellent explanation. Too bad it had to be within the context of refuting some ignorant moron who, armed with a web browser, is clearly an astronomical expert to the degree that he can confidently make these accusations.

Re:It's a photoshop job.

[Anonymous Coward]

I was worried there for a minute. I mean, if Peter T Ermit couldn't see any alternative explanations for differences between images taken from two entirely different telescopes, with entirely different focal plane arrays, and where one was in space and the other looking through the atmosphere, well then it must be NASA chicanery. What other explanation could there be??? I mean, (apart from the minor differences listed above) they are basically the same instrument!

I know how you feel. I was perusing through the Landsat data and I noticed some very clear differences in some images. NASA is up to something because this one picture they call "Green" is quite different than this other one they call "Thermal IR" even though they are of the same scene!!! I think NASA is covering something up with Photoshop---they've probably uncovered hidden nuke silos or something.

Too bad you had to retract your accusation this time, though I am confident that you'll be quick to whip it out in the future. We can all draw inspiration from vigilent watchdogs like you.

Gas

[nnnneedles]

I'm wondering, what's the brown stuff? Is that gas? That's a whole lotta gas..

Re:Gas

[exp(pi*sqrt(163))]

Dust. This galaxy is famous for having an obscuring ring of dust around it. It certainly adds to the photogenicity.

Sadly,

[pmz]

the universe turns out to be in the form of a giant Goatse.cx ascii art picture. Astronomers everywhere are thrilled about their discovery but too embarrassed to publish it.

Don't just glance...

[jafuser]

Does anyone else stare at this picture for >1 minute while readjusting their perspective?

This would be an amazing picture even if it were only fictional artwork. The fact that it's real makes it all the more amazing...

If you only glanced, then go back and pause for a moment. Make sure you view the 435kiB version so you can see the details...

Huuuuuuge

[FrostedWheat]

this magnificent galaxy is nearly one-fifth the diameter of the full moon

This reminds me of an image I seen lately, here.

It was really a suprise to learn just how big these objects are in the sky despite the unimaginable distance. That and just how dim they are! Even our own galaxy is a faint band of light despite us being right inside it. It's a shame really, imagine seeing the Andromeda galaxy like in that picture high in the sky!

Re:Huuuuuuge

[adeyadey]

Yes thats an impressive picture that make a good point. It shows that one of the best ways to see the night sky is with a pair of fairly low mag binoculars with big lenses to concentrate the light.

Oh and you need dark skies too..

Aarrk! Aarrk! Earth Humor!

[Trikenstein]

Shouldn't compressing something as large as a galaxy down that small create a quantum singularity? Aarrk! Aarrk!

Dust, and a whole bloody lot of it

[ControlFreal]

Indeed, it's dust. In order to get just a rough idea of how much dust that is, picture the following:

The Messier 104 (Sombrero) galaxy contains anywhere between 210,000,000,000 and 800,000,000,000 stars (although the latter figure seems more likely to me, mostly because the estimate is newer). That is a whole lot of mass!

Look at the image: given that the galaxy is about 50,000 lightyear across, the dust-band must be about 1,000 lightyears across. Just, for the sake of argument, assume that the dust is located in a ring with a diameter of 50,000 lightyears, 1,000 lightyears high and 1,000 lightyears thick. Then this ring has a volume of 1,000*pi*(51,000^2-50,000^2) is about 3e+11 cubic lightyears, which is 2.5e+59 cubic meters.

Is there any astronomer out there who can shed some light on the density of these clouds? Think about it: even if you assume only 1 (hydrogen) atom per square meter, there are 2.5e+59 hydrogen atoms there, which weight 4e+34 kg, and that's a very, very low estimate!

To put that into perspective: the earth weights about 6e+24 kg.

Re:Dust, and a whole bloody lot of it

[EricWright]

When I was a grad student, I did numerical simulations of supernova remnant evolution. These blasts were simulated expanding into an interstellar region of H density 1 per cc. I imagine dust clouds would be anywhere between 100 to 1000 times more dense than the "normal interstellar medium".

1 per cubic meter is FAR too low of an estimate (a million times less dense than I used, and my figure was based on published articles in The Astrophysical Journal), meaning there is probably a billion times more mass tied up in the dust clouds of M104 than your estimate. That a whole bloody, freaking, massive, gigantic, tremendous, enormous lot of dust!

Re:Dust, and a whole bloody lot of it

[ControlFreal]

I could have imagined that it would have been much more than 1 atom per cubic meter, since I thought that that would be the density of interstellar "vacuum", and the dust-clouds of course are much denser than that.

Now, I'm a bit puzzled here: I always thought that there interstellar "vacuum" had about 5 atoms per cubic meter, while your figures would imply about 10e+6 per cubic meter. Where does the difference come from? It 5 atoms/m^3 the density in intergalactic space and 1e+6 atoms/m^3 that for interstellar space in a galaxy?

Then there is another thing: I've read about molecular clouds, and that they contain about 10^21 protons per square meter. I think we can definately say that the dust band in M104 is not a molecular cloud: a density of 10^21/m^3 would imply that (in order of magnitude) ~10e+80 atoms would be in the dust band, and that would be about a billionth of the total mass in the visible universe, in one dust band in a galaxy alone. So no molecular cloud there (or at least one that's much less dense than a "typical" molecular cloud.

Your rough estimate (~1e+9 atoms/m^3) comes down to a total dust-mass, in only the visible brown band that we see, of about 4e+43 kg. This still seems high to me: the mass of the sun is 2e+31 kg, so the dust-band would weight the same as about 2e+12 suns. But there are only 8e+10 stars in that galaxy!

Shouldn't that density be much less then?

Re:Dust, and a whole bloody lot of it

[EricWright]

I don't remember the specifics, but an estimate of 5 H/cubic meter would seem to be appropriate for IGM density, as opposed to the 1 H/cc standard for ISM. The ISM figure is a total number density and is not based on visible luminosity calculations. Also, IIRC, the estimates are 8e+11 stars (800 hundred billion) in M104, not 8e+10. Finally, I don't think you remember your molecular cloud densities properly. Some of my collegues were simulating SNR shock waves impacting molecular clouds (to study the efficacy of SNRs as catalysts to stellar formation) in which a value of 10^6 H/cc (10^12 H/cubic meter, not 10^21) was used.

3D picture?

[NuShrike]

Can that Mission3-D's Photo3-D 303 kit handle this?

Then slap it into Freelancer, and I'll fly around for a look. :)