galaxies – Australian Science

Andromeda and the 13 Dwarfs

Markus — Mon, 25 Feb 2013 00:07:37 +0000

Astronomy is quite notorious for being full of things we don’t entirely understand. Sometimes it really does feel as if the closer we look at the Universe, the less it makes sense. One thing in particular which seems to constantly evade our understanding is the way in which galaxies work. A lot of very smart people spend a lot of time taking telescope observations and creating computer simulations to try and understand how exactly a galaxy can form and evolve, and every now and again someone will discover something which doesn’t seem to fit with what they were expecting. Occasionally we find something like that which is, at least in cosmic terms, right in our back yard.

The Andromeda galaxy is practically a twin sister to our own Milky Way. Slightly larger than us but slightly less massive, Andromeda lies around 2.5 million light years away, and between them Andromeda and the Milky Way dominate the local group of galaxies. But Andromeda is not without fanciful tastes – it wears a skirt over a million light years in diameter, made up of dwarf galaxies.

A recent study headed by Rodrigo Ibata at the Strasbourg Astronomical Observatory, France, and Geraint Lewis at the University of Sydney, Australia, found a host of new galaxies in the local group. The image below gives you an idea of the scale involved, but it doesn’t show the full story – There are actually over 54 galaxies in the Local Group. Andromeda is surrounded by a small swarm of 27 dwarf galaxies, and 13 of those dwarf galaxies orbit in the same plane, the same way the planets orbit the Sun. This means that Andromeda is surrounded by a disk-like shape, the largest cohesive structure in the local group. And it’s still very much a mystery as to why it exists.

Even here inside the largest galaxy for millions of light years, space is mostly empty, but the vast expanses of intergalactic space are so devoid of anything that it’s difficult to fully appreciate (to get even more perspective on this, click here and look at the full image!). But even in the face of this terrifying emptiness, galaxies live out their lives. They pull on each other and interract. They form and coalesce. Large galaxies devour smaller ones whole, and every so often, large galaxies smash together and tear each other apart. But none of the theories we have today quite explain Andromeda’s skirt.

Those 13 dwarfs orbit Andromeda once every 5.5 billion years or so, and Ibata, with his team of researchers, has suggested a couple of explanations for the disk. Firstly is that they formed in place as they are, and have been slowly twirling around Andromeda since before the Sun was born. They may have been created during a merger between two ancient galaxies, from a streamer of gas which was spun off. Or possibly, these galaxies are as old as Andromeda itself, forming at the same time amidst all of the dark matter attracted by Andromeda’s huge bulk. This would fit with the fact that those dwarf galaxies are made up of ancient stars, implying that this structure could be truly ancient.

Or perhaps it isn’t a disk at all. Perhaps we’re seeing a slew of galaxies recently pulled into Andromeda’s gravitational grip, and it’s purely by chance that they appear to be arranged into a disk shape. It’s entirely possible, and only further research will show if the disk structure is real or not. Combined with the recently discovered halo of gas surrounding the Milky Way, it seems there may be a lot lurking out there in intergalactic space that we don’t yet understand.

But either way, both of these hypotheses have problems with them. Neither is a perfect fit. In an interview, Nicolas Martin at the Strasbourg Astronomical Observatory explained that the fact that we don’t know why these galaxies are arranged the way they are is what makes this discovery so exciting;

“The presence of this thin, rotating disk of dwarf galaxies around Andromeda suggests a strong connection between the host galaxy Andromeda and its satellites. There is currently no satisfactory scenario that can explain all the properties of the satellites in the disk, but they all require a strong interplay between Andromeda and the satellites themselves.”

Image credits:
Top – Robert Gendler
Middle – Andrew Z. Colvin/Wikimedia Commons
Bottom – Rodrigo Ibata/PAndAS team

Cite this article:
Hammonds M (2013-02-25 00:07:37). Andromeda and the 13 Dwarfs. Australian Science. Retrieved: Apr 29, 2024, from http://australianscience.com.au/space/andromeda-and-the-13-dwarfs/

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Fascinating short film about NASA’s Dawn: the very beginning of us

Editorial Board — Tue, 22 Jan 2013 00:01:42 +0000

This fascinating video, narrated by Leonard Nemoy, gives you a glimpse into the origins of our solar system and NASA Dawn mission’s journey to Vesta & Ceres and its hope to unveil clues as to what was going on at the very beginning of our solar system’s formation!

NASA’s Dawn mission is a spacecraft designed to collect data from the asteroid belt. The ship itself is a marvel. Outfitted with massive solar panel wings that can power it for years, Dawn converts xenon gas into plasma, which it propels from its engine at speeds up to 78,000 miles per hour (or 21 miles per second) for maximum acceleration. In fact, Dawn is the fastest ship NASA has ever launched. Even at top speeds, Dawn required four years to reach its first stop, the asteroid Vesta, the brightest asteroid in the solar system and the only one visible to the naked eye. Departing Earth in 2007, the ship reached Vesta in July of 2011 and departed last September for the asteroid Ceres, which it will reach in February of 2015. Via OpenCulture.

For those visually driven – please take a look at the beautiful interactive map of our stellar neighborhood. With over 100,000 stars in an interactive visualisation, you can take a walk through the stellar neighborhood.

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A long time ago in a galaxy far, far away

Markus — Tue, 25 Sep 2012 03:37:38 +0000

Feast your eyes on this image…

Image credit: The CLASH team/Space Telescope Science Institute

The tiny object in that inset may not look like much. A blurry smudge of red pixels. Not nearly as dramatic as the stunning bouquet of galaxies all around it. But in astronomy, not everything is quite so straightforward. That small red smudge is probably the most exciting thing in this whole image. You see, it too is a galaxy. An unimaginably ancient one.

An ultraviolet image of the nearby Andromeda Galaxy – possibly similar to what we might see of MACS 1149-JD if we could get a more detailed view... Credit: NASA/Swift/Stefan Immler (GSFC) and Erin Grand (UMCP)

The light that made this unassuming red dot left its source less than 500 million years after the Big Bang and the birth of the Universe. The photons that make up that light have been travelling for over 13.2 billion years. This galaxy was blazing brightly as the oldest known stars in our own galaxy, the Milky Way, were just starting to shine. Back when the gas which would one day become the Sun was still drifting silently amongst stars which are now long dead, and before planet Earth was even a whisper of interstellar dust. Before a massive star forged the iron atoms in your blood, and before a supernova scattered those atoms into space. Before anything we know from the world around us existed, even the stars we see as we look up to the night sky, this galaxy was shining in the dark.

The Universe was a much smaller place back then. Over the billions of years these photons have been travelling, the Universe itself has expanded with them in the midst of it – stretching them out, redshifting them to longer and longer wavelengths. The light we see here as red was probably ultraviolet once, when it left the galaxy which created it.

Ancient galaxies like these are difficult to see, purely because they’re so distant. So few photons make it this far that only the most sensitive telescopes can make them out, and even then they need a helping hand. The bloom of galaxies in this image is a massive galaxy cluster called MACS J1149+2223. A collection of galaxies bound together by gravity, clusters like these are some of the largest and most massive objects in the Universe. With that much mass gathered together, gravity starts to do some interesting things, and one of the most interesting is gravitational lensing. Because the gravity of all of those galaxies distorts spacetime, it actually causes the space around the galaxies to act like a titanic lens. A gravitational lens. The ancient red galaxy in this image is only visible because it’s magnified, not only by the Hubble Space Telescope, but by that gravitational lens too.

It would be naive to assume that this galaxy, dubbed MACS 1149-JD, is special somehow. Instead, it’s most likely to be one of a huge number of primordial galaxies. Except that this one just happened to be in the right place at the right time. A whole population of these ancient galaxies were likely shining brightly at the time, full of hot stars which were driving the reionisation epoch – the time when the Universe went from being an opaque, dark fog, to a clear place where photons could travel long distances. The photons in this image may well have been some of the first photons to have travelled through that ancient and newly transparent Universe.

The scientific paper is available from Nature – DOI: 10.1038/nature11446

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