APOD: Ultraviolet Andromeda (2010 Oct 27)

[APOD Robot]

Ultraviolet Andromeda

Explanation: This stunning vista represents the highest resolution image ever made of the Andromeda Galaxy (aka M31) at ultraviolet wavelengths. Recorded by NASA's Swift satellite, the mosaic is composed of 330 individual images covering a region 200,000 light-years wide. It shows about 20,000 sources, dominated by hot, young stars and dense star clusters that radiate strongly in energetic ultraviolet light. Of course, the Andromeda Galaxy is the closest large spiral galaxy to our own Milky Way, at a distance of some 2.5 million light-years. Just slide your cursor over the image to compare the appearance of this gorgeous island universe in optical light with its ultraviolet portrait.

<< Previous APOD

Discuss Any APOD

Next APOD >>

[/b]

[neufer]

Discussion

Click to play embedded YouTube video.

[Ann]

Art! We've got an ultraviolet image for once. Even better and even more unusual, it's an ultraviolet image of a spiral galaxy and not, say, of the Sun. And hey, you start talking infrared???

In September and October there have been at least five infrared light APODs, September 14 (An Extraordinary Spiral from LL Pegasi), September 27 (The Dancing Auroras of Saturn - yep - they were taken in infrared light), September 28 (Venus South Polar Vortex), September 30 (Coreshine from a Dark Cloud) and October 15 (Vista with NGC 2170).

As far as I have noticed, there have been no ultraviolet images posted during this same period, certainly no ultraviolet images of spiral galaxies. Now let me savor this ultraviolettie for once!!!



Ultra Violeta, yeah!

Ann

[skim]

I would really love to see this image in 3d

[owlice]

What a stunning image! And Art, the video was great; thanks for posting it! The combination of the infrared and ultraviolet images of the galaxy was beautiful, too! It doesn't really matter the wavelength: Andromeda is pretty in all of them.

[TheSpam]

Question: There is a rather large round source of light on the Ultraviolet image seen clearly just slightly below middle on the far left. It appears much smaller in the optical light image (1/4 size roughly).

Any explanation for this? Larger/Brighter in Ultraviolet than in optical, what would that suggest?

If your having trouble finding it quickly mouse over the two images repeatedly, it should become apparent fairly quickly.

[Hannah's Dad]

Approximately how many forground milky way stars are present in the image? How can one distinguish smaller sources in the Milky Way foreground from larger sources that may be in Andromeda?

[neufer]

Approximately how many foreground milky way stars are present in the image? How can one distinguish smaller sources in the Milky Way foreground from larger sources that may be in Andromeda?

Milky Way foreground stars show up as bright isolated spots in the visible with a relatively homogeneous coverage.
There are a couple of thousand of them.

[neufer]

[img3="A Galaxy Evolution Explorer observation of M31 with near ultraviolet shown by red and far ultraviolet shown by blue. M32, a dwarf elliptical galaxy directly below the central bulge and just outside the spiral arms, and M110, above and to the right of the center. M110 has an unusual far ultraviolet bright core in an otherwise "red", old star halo."]http://upload.wikimedia.org/wikipedia/c ... galaxy.jpg[/img3]

Question: There is a rather large round source of light on the Ultraviolet image seen clearly just slightly below middle on the far left.
It appears much smaller in the optical light image (1/4 size roughly).

A Milky Way blue giant star?

Note that it is rather reddish in this Galex ultraviolet image=>

Any explanation for this? Larger/Brighter in Ultraviolet than in optical, what would that suggest?

OB stars would be brighter in the near ultraviolet.

[orin stepanek]

http://astrophysics.gsfc.nasa.gov/outre ... new-light/
I get a not available on this server from this url!

[neufer]

Art, the video was great; thanks for posting it!

I'm ordering pepperoni, mushrooms, and dwarf galaxies on my next pizza. (MMMMMMM....)

[Guest]

Wow a twin galaxy to http://apod.nasa.gov/apod/ap090917.html

[biddie67]

I'm ordering pepperoni, mushrooms, and dwarf galaxies on my next pizza. (MMMMMMM....)

I understand that dwarf galaxies are really crunchy and hotter than jalapenos!!! Proceed with care!

[biddie67]

I'd love to have a series of posters to hang on the wall that showed Andromeda as seen in all the different wavelengths - they would make a fine display.

[owlice]

I'd love to have a series of posters to hang on the wall that showed Andromeda as seen in all the different wavelengths - they would make a fine display.

What a great idea for a thread: a series of Andromeda images! Thanks!!

[Ann]

Question: There is a rather large round source of light on the Ultraviolet image seen clearly just slightly below middle on the far left. It appears much smaller in the optical light image (1/4 size roughly).

Any explanation for this? Larger/Brighter in Ultraviolet than in optical, what would that suggest?

If your having trouble finding it quickly mouse over the two images repeatedly, it should become apparent fairly quickly.

I know what star you mean. I've been looking for it with my astronomy software, but I can't find anything obvious.

But take a look at this GALEX image:

Click to view full size image

Can you see a very blue-looking star below and to the left of Andromeda at about a 7.30 position? Okay, now take a look at this visual-light image of Andromeda:



Can you see a very red star above and to the left of Andromeda? I believe that the red star in this picture is the same as the blue star in the GALEX image. But how can a star that is very red visually be very blue in ultraviolet light? Is that even possible?

Apparently so. The star in question would be EG Andromedae, a cool red M giant. EG Andromedae is very far away, possibly as much as 2,000 light-years, and it may be around 500 times as bright as the Sun in visual light. That, of course, means that it would be even brighter in infrared light, given the fact that this star is so cool. Its color index is 1.613 ± 0.014, which is a lot.

So EG Andromeda is a visually very red and cool star. But it is also a massive star, and its core is blazingly hot. Even though EG Andromedae is visually a red star, its core emits a lot of far ultraviolet light, and the star will show up as strikingly blue in a GALEX image.

Ann

[TheSpam]

Thanks to both neufer and Ann for replying to my question. I found a 1983 article http://adsabs.harvard.edu/full/1983PASP...95..759K that confirms Ann is correct and the star is EG And. Very Cool!

[bystander]

http://astrophysics.gsfc.nasa.gov/outre ... new-light/
I get a not available on this server from this url!

There's a space in the URL that is not supposed to be there. Try:
http://astrophysics.gsfc.nasa.gov/outre ... new-light/

[geoffrey.landis]

On the question of identification, what it is in the lower right? Of the two stars in the lower right, one has a diffuse hollow ring near, but not quite centered on, it in the ultraviolet image. It looks like an artifact, but if so, it seems to be the only star with such an artifact. Is this real?

[CBridge]

What an absolutely stunning photo! It reminds me of the photos of the earth taken at night showing all the lights of the various cities.

[neufer]

I believe that the red star in this picture is the same as the blue star in the GALEX image. But how can a star that is very red visually be very blue in ultraviolet light? Is that even possible?

Apparently so. The star in question would be EG Andromedae, a cool red M giant. EG Andromedae is very far away, possibly as much as 2,000 light-years, and it may be around 500 times as bright as the Sun in visual light. That, of course, means that it would be even brighter in infrared light, given the fact that this star is so cool. Its color index is 1.613 ± 0.014, which is a lot.

So EG Andromeda is a visually very red and cool star. But it is also a massive star, and its core is blazingly hot. Even though EG Andromedae is visually a red star, its core emits a lot of far ultraviolet light, and the star will show up as strikingly blue in a GALEX image.

Its core is blazingly hot? You can see the core??

• http://www.youtube.com/watch?v=1Dk83DYRgp0
  
  There once was an M giant in Andromeda
  Who watched little boys as they played with their
  Marbles and toys as in days of old yore
  And for a companion he had a white dwarf.

EG Andromeda is a cool red M giant with a very hot companion:

SYNTHETIC SPECTRAL ANALYSIS OF THE HOT COMPONENT IN THE S-TYPE SYMBIOTIC VARIABLE EG ANDROMEDAE
KELLY KOLB, JOLEEN MILLER, AND EDWARD M. SION
Department of Astronomy and Astrophysics, Villanova University.

AND JOANNA MIKOłAJEWSKA
Centrum Astronomiczne im. Mikołaja Kopernika, Polska Akademia Nauk, ulica Bartycka 18, PL-00-716 Warszawa, Poland.

Received 2004 March 29; accepted 2004 June 25

ABSTRACT

We have applied grids of non-LTE (NLTE) high-gravity model atmospheres and optically thick accretion disk models for the first time to archival IUE and FUSE spectra of the S-type symbiotic variable EG Andromedae taken at superior spectroscopic conjunction, when Rayleigh scattering should be minimal and the hot component is viewed in front of the red giant. For EG And's widely accepted, published hot-component mass, orbital inclination, and distance from the Hipparcos parallax, we find that hot, high-gravity, NLTE photosphere model fits to the IUE spectra yield distances from the best-fitting models that agree with the Hipparcos parallax distance, but at temperatures substantially lower than the modified Zanstra temperatures. NLTE fits to an archival FUSE spectrum taken at the same orbital phase as the IUE spectra yield the same temperature as the IUE temperature (50,000 K). However, for the same hot-component mass, inclination, and parallax-derived distance, accretion disk models at moderately high inclinations, ∼60°–75°, with accretion rates from 1 × 10-8 to 1 × 10-9 M⊙ yr-1 for white dwarf masses Mwd = 0.4 M⊙ yield distances grossly smaller than the distance from the Hipparcos parallax. Therefore, we rule out an accretion disk as the dominant source of the far-UV flux. Our findings support a hot bare white dwarf as the dominant source of far-UV flux.

[mexhunter]

Spitzer's and now NASA's Swift satellite has given us the chance to see otherwise deep space, not as artistic as other telescopes, although I suppose most disturbing to professional astronomers.
Greetings
César

[crisdavid2]

This picture have two green paralel lines at left side. What is it?.

[RandyT5194]

What great fun, mousing over the photo, and comparing the visible vs. UV
images.

One feature was particularly striking to me: at about 4 o'clock from the
galactic center are two bright stars. The brighter of the two, the one
that's the "left-most" of them, has 3 or 4 very bright (in UV) objects in a
straight line, or perhaps in an L shape. Only one of the objects is
apparent on the visible light image.

They seem outside the large arm where all the fun hot stuff is, and are one
of the few objects outside the large arms that pop in UV but not in visible
light.

Any idea what they are?

[Ann]

Its core is blazingly hot? You can see the core??

Eh... no, I can't....

But the core of a red giant is hot! That sets it apart from the core of a red dwarf, which is, as stellar cores go, measly and cool.

When I look at some info on red supergiants, such as Betelgeuse, I'm often told that this star displays ultraviolet FeII emission. Personally I've taken this to mean that red giant stars, and certainly red supergiants, are ultraviolet emitters that would show up better than most stars in ultraviolet images. (I also thought that this FeII ultraviolet emission wouldn't be there if these cool stars didn't have such hot cores... Any comments on that?)

As for EG And being a symbiotic star, my software has no information on that. Nowhere does it say that EG And is multiple at all. But it makes excellent sense that it is, so thank you very much for providing that information, Art!

Ann