The galaxy we live in, the Milky Way, is a large spiral galaxy that lives in a small cluster of other galaxies called the Local Group. The other big member is the Andromeda galaxy, located about 2.5 million light years away. That’s a long way off, but we’ve known for a long time that Andromeda is heading more or less toward us at a speed of roughly 100 km/sec (60 miles/second).
The question is, is it headed directly at us, or does it have some "sideways" motion and will miss us? New results announced today by astronomers using Hubble show that — gulp! — Andromeda is headed right down our throats!
But don’t panic. It won’t happen for nearly 4 billion years.
This is a pretty cool result. They used Hubble to look at stars in Andromeda’s halo, the extended fuzzy region outside the main body of the galaxy. By very carefully measuring the positions of the stars over seven years, they could directly measure the motion of those stars. Extrapolating that into the future has allowed the motion of the Andromeda galaxy itself to be determined for the first time.
So what’s going to happen?
First, watch this awesome video of the collision based on the observations:
So here are the details:
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
- 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?
Every now and again, a Hubble image will kick me back with a wave of nostalgia.
Most Hubble pictures are of specific objects with which I’m not familiar, some galaxy or cluster I’ve never even heard of. Sometimes the great observatory is pointed at a target I do know from my own youth as an amateur astronomer, something I’ve seen myself through my telescope.
And sometimes it’s something with a more personal connection, a galaxy I’ve actually studied, and which reminds me of old friends, figuratively and literally… like this incredible picture of the halo of the Andromeda Galaxy:
[Click to unenchainedmaidenate.] Lovely, isn’t it?
The Andromeda Galaxy is the nearest big spiral like our own. It’s just under 3 million light years away, as big as the Milky Way (even maybe a shade bigger), and bright enough to be seen easily by the naked eye in a dark site. I’ve spent hours looking at it through binoculars and my own telescope. This picture — one of four peering at this gigantic island universe — is looking into the galaxy’s halo, the cloud of stars surrounding the main disk.
You can see right through it, to galaxies beyond. The bigger ones you see are probably hundreds of millions of light years away, but the smaller, red ones? Those are billions of light years away, the light you’re seeing here having left those distant galaxies before the Earth was even born.
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
Was the Andromeda Galaxy, the largest and most massive galaxy in our local neighborhood, shaped into its current structure due to a monstrous collision over 6 billion years ago? According to a new study by some French astronomers, the answer is oui.
They created a lovely animation based on the model. It shows the collision of the two galaxies and how they interact:
Wow! You can see how the galaxies get disrupted, and perhaps get something of a feel for just how violent and incredible an event on this scale can be.
Using a sophisticated computer code that models the gravitational and fluid (pedantic: hydrodynamical) interaction between stars, gas, dust, and dark matter, they found that an ancient and massive collision between a galaxy a bit bigger than our Milky Way, and a smaller one about 1/3 the mass, reproduces a large amount of the structure we see in Andromeda today. That includes "…the large thin disk including its giant ring of gas and dust, the massive central bulge, the gigantic thick disk, the giant stream of old stars, as well as many other stellar streams discovered in the galaxy halo" according to the press release (the paper itself is in French).