Star Birth and Death in the Andromeda Galaxy


To the naked eye, the Andromeda galaxy appears as a smudge of light in the night sky. But to the combined powers of the Herschel and XMM-Newton space observatories, these new images put Andromeda in a new light! Together, the images provide some of the most detailed looks at the closest galaxy to our own. In infrared wavelengths, Herschel sees rings of star formation and XMM-Newton shows dying stars shining X-rays into space.

During Christmas 2010, the two ESA space observatories targeted Andromeda, a.k.a. M31.

Andromeda is about twice as big as the Milky Way but very similar in many ways. Both contain several hundred billion stars. Currently, Andromeda is about 2.2 million light years away from us but the gap is closing at 500,000 km/hour. The two galaxies are on a collision course! In about 3 billion years, the two galaxies will collide, and then over a span of 1 billion years or so after a very intricate gravitational dance, they will merge to form an elliptical galaxy.

Let’s look at each of the images:

Herschel’s view in far-infrared:

Andromeda in far-infrared from Herschel. Credits: ESA/Herschel/PACS/SPIRE/J. Fritz, U. Gent

Sensitive to far-infrared light, Herschel sees clouds of cool dust and gas where stars can form. Inside these clouds are many dusty cocoons containing forming stars, each star pulling itself together in a slow gravitational process that can last for hundreds of millions of years. Once a star reaches a high enough density, it will begin to shine at optical wavelengths. It will emerge from its birth cloud and become visible to ordinary telescopes.

Many galaxies are spiral in shape but Andromeda is interesting because it shows a large ring of dust about 75,000 light-years across encircling the center of the galaxy. Some astronomers speculate that this dust ring may have been formed in a recent collision with another galaxy. This new Herschel image reveals yet more intricate details, with at least five concentric rings of star-forming dust visible.

XMM Newton’s view in X-rays

XMM Newton's view in X-Ray. Credits: ESA/XMM-Newton/EPIC/W. Pietsch, MPE

Superimposed on the infrared image is an X-ray view taken almost simultaneously by ESA’s XMM-Newton observatory. Whereas the infrared shows the beginnings of star formation, X-rays usually show the endpoints of stellar evolution.

XMM-Newton highlights hundreds of X-ray sources within Andromeda, many of them clustered around the centre, where the stars are naturally found to be more crowded together. Some of these are shockwaves and debris rolling through space from exploded stars, others are pairs of stars locked in a gravitational fight to the death.

In these deadly embraces, one star has already died and is pulling gas from its still-living companion. As the gas falls through space, it heats up and gives off X-rays. The living star will eventually be greatly depleted, having much of its mass torn from it by the stronger gravity of its denser partner. As the stellar corpse wraps itself in this stolen gas, it could explode.

Together, the infrared and X-ray images show information that is impossible to collect from the ground because these wavelengths are absorbed by Earth’s atmosphere. Visible light shows us the adult stars, whereas infrared gives us the youngsters and X-rays show those in their death throes.

15 Replies to “Star Birth and Death in the Andromeda Galaxy”

  1. I’m still a bit of a novice astronomy buff, so I may be completely off-base, but is there a massive amount of gravitational lensing around the galactic core in the X-ray image? To me it looks almost like someone put a small magnifying glass over the center of the galaxy in that image.

    1. Good observation! There does seem to be a trend toward a circular elongation in some of the objects nearer the core. Could be a detector artifact? or perhaps a gravity wave artifact? or… you may be on to something!

    2. I suspect this lens-like appearance is an artifact of data processing. Gravitational lensing is not sensitive to the wavelength of photons, so if this were present it would appear in all spectra observed.


      1. Ok cool, thanks. I was thinking that real lensing would be visible in the other spectra, and couldn’t see any similar effect in the IR images, but I wasn’t sure. The circular “distortion” isn’t actually uniform, now that I look closer, so I suppose it could just be an illusion caused by the perspective, or a processing artifact, as you said.

  2. the answer is probably none of them..and neither (the good-old-funny) Dark Matter..a new theory would explain a lot about galaxy dynamics and enlighten all of us ;-))
    Feb 14 is St. Valentines day right ? maybe we should wait for that..

  3. Excellent images Nancy. I sent an e-mail to you with a link to the Hydrogen Alpha image by Jon Talbot. He gave his permission to share it. I’d like to post the URL if it’s okay with you.

  4. Andromeda is about twice as big as the Milky Way but very similar in many ways.

    Huh? It is roughly “twice as big” in number of stars AFAIU, but I thought the new results were that they are twins in mass:

    “Mass estimates for the Andromeda halo (including dark matter) give a value of approximately 1.23×1012 M?[31] (or 1.2 million million solar masses) compared to 1.9×1012 M? for the Milky Way. Thus M31 may be less massive than our own galaxy, although the error range is still too large to say for certain. Even so, the masses of the Milky Way and M31 are comparable, and M31’s spheroid actually has a higher stellar density than that of the Milky Way.[32]

    In particular, M31 appears to have significantly more common stars than the Milky Way, and the estimated luminosity of M31, ~2.6×1010 L?, is about 25% higher than that of our own galaxy.[33] However the rate of star formation in the Milky Way is much higher, with M31 only producing about one solar mass per year compared to 3–5 solar masses for the Milky Way. The rate of supernovae in the Milky Way is also double that of M31.[34] This suggests that M31 once experienced a great star formation phase, but is now in a relative state of quiescence, whereas the Milky Way is experiencing more active star formation.[33] Should this continue, the luminosity in the Milky Way may eventually overtake that of M31.”

    1. Also, that recent star formation of Andromeda would be a likely consequence of a putative recent galaxy collision, no? The big brother Milky Way is just waiting for the head on collision that is in the works, and if not before _then_ you will see stars!

      1. Sorry, I don’t know why I inserted “recent” in star formation. Talking about conforming reality to your expectations!

  5. Great far-IR and X-ray photos !!!

    As each different ‘octave’ of the EM Spectrum gives us a different piece of the puzzle of what’s happening out there, we need all 20 octaves of the EM Spectrum in discrete separate photos before we’ll have the full picture !

    The X-ray ‘bubble’ surrounding M31’s core is most interesting !!!

    As knowing the difference between ‘thermal’ atomic electron energy and ‘electron temperature’ synchrotron emission electron energy, therein lies the tale of are these ‘dust grains’ glowing in ‘thermal’ temperature, or are they synchrotron electron far-IR emissions from magnetic field motion electrons ? (in the far-IR photo)

    And are they thermal X-ray induced emissions or are they synchrotron electron X-ray emissions ? (in the X-ray photo)

    Confusing the former for the latter will lead to catastrophically erroneous conclusions about what’s happening there.

    1. I have a link to another that is interesting and am waiting for a moderator to give permission to share it here. I know others just post with links but, I want to follow the rules.

  6. I am fascinated with filtering techniques. Here’s the link to the image I was asking permission to post. The remnant at the nucleus shows up nicely here, I think.

  7. I apologize profusely in advance for this, it is only my 2nd post and already I’m violating the rules of etiquette if not the site. However the subject matter is very tenuously related to this topic so hopefully I won’t have to get a taste the banning stick.

    In the topic “Astronomy Without A Telescope – Secular Evolution”

    Lawrence B. Crowell Wrote “The Milky Way and Andromeda are set to collide in 2 billion years, to form an elliptical galaxy.. It is not unreasonable to think that 2 billion years beyond then there will be a mega spiral galaxy as a result.”

    My question was that After the MW and Andromeda merge the result will be a elliptical galaxy. I’m with you so far. But you are saying that at some undefined time in the future the galaxy will return to being a spiral? How is this possible? I thought that the second law of thermodynamics applied to Astrophysics as well? In a closed system (our two galaxies) entropy will always increase and leave the combined state in a higher state of disorder than the sum of the two initial systems.

    I always thought that this was one of the quasi inescapable truths right up there with no FTL travel?

    thx and I apologize again for high jacking this topic,


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