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.

[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.

Aye, Cap'n!

[rudy_wayne]

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

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.

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: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!