Tag: M31

Andromeda's majestic spray of billions of hot stars

By Phil Plait | May 18, 2012 11:33 am

Well, what can I say about this devastating and jaw-dropping picture of our nearest spiral neighbor, the Andromeda Galaxy?

[Click to massive chainedmaidenate. Do it!]

Well, I could start with HOLY HALEAKALA!

This image is a collection of 11 separate observations of Andromeda taken by NASA’s GALEX satellite. Launched in 2003, GALEX (which stands for Galaxy Evolution Explorer) scans the sky in ultraviolet light, specifically targeting galaxies. Hot stars produce UV light, and so does the gas it illuminates, so by looking in the ultraviolet astronomers can learn about how galaxies are constructed. In the decade since its launch, GALEX has been phenomenally successful, cataloging hundreds of millions of galaxies, some as far as ten billion light years away!

This image of Andromeda is simply stunning. It’s comprised of two colors: what you see here as blue is higher-energy ultraviolet light, and red is lower energy (closer to the kind of light we see). Right away you can see that objects emitting the higher-energy UV are confined to the spiral arms, and lower-energy emitters are spread out across the galaxy. That’s exactly what I would expect: massive stars, the kind that really blast out UV, don’t live very long. They’re born, live out their short lives, and die (as supernovae) pretty much near the spot where they formed, which is in spiral arms. Lower mass stars live long enough to gradually move away from their nurseries, populating the rest of the galaxy.

Also, star formation at the very center of the galaxy probably occurred long ago and shut down, so we don’t see many or any massive stars there.

One thing I didn’t know is that the arms of Andromeda are more like rings! The galaxy is at such a narrow angle that it’s hard to tell, but if you trace the blue emission, the pattern does look more like a ring than a spiral. This jibes with earlier images in infrared taken by Spitzer Space Telescope (which I’ve inset here) and a huge and incredibly beautiful newer one taken with ESA’s Herschel far-infrared telescope (and OMFSM you want to click that link).

From what I’ve read, it’s not clear why the spiral arms appear to be more ring-like. Which I love. Why? Because Andromeda is the nearest big spiral galaxy in the sky, a mere 2.5 or so million light years away. It’s easily visible to the naked eye from a dark site, and I’ve seen it myself countless times using my own eyes, binoculars, and telescopes ranging from small ones up to Hubble. Yet there it is, in all its huge and obvious splendor and beauty, still able to surprise me. That rocks.

And a note about GALEX: NASA recently handed off its operations to Caltech, a very unusual move. The satellite was put into standby mode in February, and I was worried it would be shut down permanently. However, Caltech signed a three-year agreement with NASA — while NASA still owns the satellite, Caltech will now be in control of GALEX’s science mission, managing and operating it. At the end of the agreement it can be renegotiated if GALEX is still in good operating condition. This is an interesting idea, and I’m not sure how I feel about it. I love that GALEX gets to continue operations, but handing off science missions to private groups makes me a little uneasy. In this particular case I think it’s fine — Caltech is a research institute after all — but the precedent may have unforeseen consequences. We’ll see.

Still and all, it’s good to see new life breathed into an important and wonderful instrument like GALEX. I certainly hope it will continue to produce cutting-edge science for years to come… as well as amazingly beautiful images like this one.

Image credit: NASA/JPL-Caltech


Related Posts:

The cold arms and hot, hot heart of the fuzzy maiden
The first spectacular views of the sky from WISE
A Swift view of Andromeda
Andromeda’s warm glow
Andromeda: born out of a massive collision?

The cold arms and hot, hot heart of the fuzzy maiden

By Phil Plait | January 5, 2011 12:15 pm

Hot (and cold) on the heels of my posting the infrared view of the nearby spiral M33, the European Space Agency just published this incredible picture of our other spiral neighbor, M31, the Andromeda Galaxy!

[Click to galactinate.]

Oh my. This is a composite of two orbiting observatory images: the far infrared using Herschel (colored orange), and the X-ray emission using XMM-Newton (blue). There’s so much to see! That’s not surprising, since at 2.5 million light years away, Andromeda is the closest big galaxy to us, and presents itself with loads of detail.

First, shown here is Robert Gendler’s magnificent visible-light image of the galaxy. You can see it’s tilted almost edge-on to us, but you can see the central bulge of old stars, the spiral arms winding out, the dark lanes of dust. This image has roughly the same orientation and border as the big one above, so you can compare them.

The infrared observations trace the presence of cold dust, created when stars are born and when they die. And by cold, I mean cold: much of it is just a few degrees above absolute zero. That dust is opaque in visible light, as you can see in Gendler’s shot. But it glows in infrared! The X-rays, on the other hand, are from incredibly hot gas heated to millions of degrees by neutron stars, black holes, and newly-born massive stars; you can see several individual objects in the galaxy’s core. Read More

A WISE view of a small neighbor

By Phil Plait | January 4, 2011 7:00 am

What shall be the first astronomical object to grace this blog in 2011*? With a whole sky to choose from, why not use an old friend, but seen in a surprisingly new way? So I present to you the nearby Triangulum Galaxy, M33, as seen by the orbiting far-infrared telescope WISE:

Yeah, that’ll do! Click to galactinate.

M33 is familiar to pretty much any serious amateur astronomer north of the Equator. It’s not that far in the sky from its bigger buddy M31, the Andromeda Galaxy, and in fact isn’t terribly far in space either; Andromeda is about 2.5 million light years away, while M33 is about 3 million. M33 is a spiral galaxy as well, and one of the closest to us.

Andromeda is probably the most well-known galaxy in the sky. So why is M33 so less famous? Mostly because it’s smaller; Andromeda and the Milky Way are roughly the same size (so close, in fact, that astronomers have been arguing for decades over which is the beefier of the two, and the title has swapped back and forth many times), but M33 is only half our size. Also, it’s more face-on to us, spreading its light out, making it actually a somewhat tough object to see. I’ve seen it in binoculars from dark sites, but it’s only marginally brighter than the sky background.

In the WISE image, blue and cyan are from infrared light at 3.4 and 4.6 microns (roughly 5 and 6.5 times the reddest light your eye can see). That comes mostly from stars. Green and red are IR at 12 and 22 microns, much farther in the infrared, and comes from cooler material like interstellar dust, which is opaque to visible light.

Read More

CATEGORIZED UNDER: Astronomy, Pretty pictures
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