Astronomers Discover New 'Fossil Galaxy' Buried Deep Within the Milky Way (phys.org) 24
fahrbot-bot shares a report from Phys.Org: Scientists working with data from the Sloan Digital Sky Surveys' Apache Point Observatory Galactic Evolution Experiment (APOGEE) have discovered a 'fossil galaxy' hidden in the depths of our own Milky Way. The proposed fossil galaxy may have collided with the Milky Way ten billion years ago, when our galaxy was still in its infancy. Astronomers named it Heracles, after the ancient Greek hero who received the gift of immortality when the Milky Way was created.
The remnants of Heracles account for about one third of the Milky Way's spherical halo. But if stars and gas from Heracles make up such a large percentage of the galactic halo, why didn't we see it before? The answer lies in its location deep inside the Milky Way. "To find a fossil galaxy like this one, we had to look at the detailed chemical makeup and motions of tens of thousands of stars," says Ricardo Schiavon from Liverpool John Moores University (LJMU) in the UK, a key member of the research team. "That is especially hard to do for stars in the center of the Milky Way, because they are hidden from view by clouds of interstellar dust. APOGEE lets us pierce through that dust and see deeper into the heart of the Milky Way than ever before." APOGEE does this by taking spectra of stars in near-infrared light, instead of visible light, which gets obscured by dust. Over its ten-year observational life, APOGEE has measured spectra for more than half a million stars all across the Milky Way, including its previously dust-obscured core.
To separate stars belonging to Heracles from those of the original Milky Way, the team made use of both chemical compositions and velocities of stars measured by the APOGEE instrument. [...] Stars originally belonging to Heracles account for roughly one third of the mass of the entire Milky Way halo today -- meaning that this newly-discovered ancient collision must have been a major event in the history of our galaxy. That suggests that our galaxy may be unusual, since most similar massive spiral galaxies had much calmer early lives. The findings have been reported in Monthly Notices of the Royal Astronomical Society.
The remnants of Heracles account for about one third of the Milky Way's spherical halo. But if stars and gas from Heracles make up such a large percentage of the galactic halo, why didn't we see it before? The answer lies in its location deep inside the Milky Way. "To find a fossil galaxy like this one, we had to look at the detailed chemical makeup and motions of tens of thousands of stars," says Ricardo Schiavon from Liverpool John Moores University (LJMU) in the UK, a key member of the research team. "That is especially hard to do for stars in the center of the Milky Way, because they are hidden from view by clouds of interstellar dust. APOGEE lets us pierce through that dust and see deeper into the heart of the Milky Way than ever before." APOGEE does this by taking spectra of stars in near-infrared light, instead of visible light, which gets obscured by dust. Over its ten-year observational life, APOGEE has measured spectra for more than half a million stars all across the Milky Way, including its previously dust-obscured core.
To separate stars belonging to Heracles from those of the original Milky Way, the team made use of both chemical compositions and velocities of stars measured by the APOGEE instrument. [...] Stars originally belonging to Heracles account for roughly one third of the mass of the entire Milky Way halo today -- meaning that this newly-discovered ancient collision must have been a major event in the history of our galaxy. That suggests that our galaxy may be unusual, since most similar massive spiral galaxies had much calmer early lives. The findings have been reported in Monthly Notices of the Royal Astronomical Society.
elliptical (Score:4, Interesting)
I thought collisions usually create an elliptical galaxy, erasing the spiral nature. Perhaps this immigrant galaxy wasn't big enough to ellipticise us entirely, just the core.
There seems to be a threshold because one doesn't see many galaxies that are say 80% elliptical (fuzzy and round) and 20% spiral. M81 seems to be about the maximum of hybrids in terms of round middles. The visible part is about 40% round/fuzzy and 60% spiral (although processing and/or different filters show somewhat different mixes).
If the colliding galaxy were just slightly bigger, it would perhaps have turned M81 into a full out elliptical, and that's why around 40% seems to be about the max mix.
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I thought collisions usually create an elliptical galaxy, erasing the spiral nature.
The current state of thought on what happens is that if you get _lots_ of mergers, the resulting thing is indeed a giant elliptical. If you take several of your bog-standard dwarf ellipticals (which, like tiny red dwarf stars, seem to be the most common thing out there), you'll get a spiral. It's entirely possible that this is the way you get any medium sized spiral galaxies at all. So, glom together the Milky Way plus Andromeda, then toss in M33 and everything else in the vicinity, and you might just be
as a tree falls, one hand claps (Score:2)
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If galaxies merge and there are no sentient beings to see it, do they really merge?
Yes, because sentient beings may evolve 10 billion years later and observe the aftermath.
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Oh, and I suppose this record of a "fossil" galaxy provides credence to this "evolution" theory of yours?
Keep Calm and Carry On (Score:2)
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> Science is a delicate calling and can easily be corrupted.
That is because by definition Science is amoral: Observe. Hypothesize. Experiment. Rinse and repeat.
By being 100% focused on removing falsehood as ONE way to seek Truth, Science doesn't say anything about whether the process used to arrive at the answers is moral or immoral.
As famously said in Jurassic Park by the exchange between John Hammond (Lord Richard Attenborough) and Dr. Ian Malcolm (Jeff Goldblum):
Donald Gennaro: It's hardly appropria
Just relax, it won't hurt I promise (Score:5, Funny)
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It will in time. We are scheduled for a collision and merger in about 4.5 billion years. Set your watch.
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Eddore. Any day now.
Milky Way Geometry (Score:4, Interesting)
We know the overall shape of the Milky Way galaxy based on dozens if not hundreds of other research projects, so we have a reasonably good idea of the size and shape of our galactic home. What we’re told is that the Milky Way is a more-or-less entirely ‘normal’ galaxy. We see galactic arms - areas with stars packed more densely - radiating out from the galactic core - and we are told this is entirely normal because we see it across the universe.
But a merger with Heracles, a galaxy which we’re told accounts for a third of the stars in the Milky Way halo, sounds like a pretty major event to me.
So what I’d like to better understand is how the Milky Way has managed to retain such a relatively uniform galactic shape after such a significant merger? Everything we know about galactic collisions would seem to suggest that the result would be, well, a bit of a mess.
Could this merger explain the presence of the Milky Way’s arms? Could the calculations be off? Is it simply the fact that the resultant merged galaxy has had billions of years to “settle down”? Something else? Very interested to learn if anyone can explain how something this significant has not had a larger long-term impact.
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Because maybe the relatively uniform shape formed (or re-formed) after the significant merger.
Which is, to a second or third approximation, the standard model of spiral formation. The spiral structure visible in "spiral" galaxies is a dynamic structure, which is formed and maintained by resonant pressure waves within the disc of the galaxy. If th
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My non-academic understanding of star formation and galaxy formation had it that a star forms from, essentially, a cloud of hydrogen gas... which itself formed from the cooling quark-gluon plasma post-Big Bang. As individual hydrogen atoms came in to existence and formed molecules, their distribution in space, being random, was implicitly ever-so-slightly non-uniform. This caused certain molecules to move together thanks to the effects of gravity, which in turn caused "gaseous clumping", whic
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Didn't have a link in it. I'm going to
HUH! (Score:2)
"NEW Fossil" is oxymoronic.
"newly discovered evidence of an ancient" (Score:2)
substitute "newly discovered evidence of an ancient" or such then.
funny your comment matches your name
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Thanks for noticing!
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... that is fairly well established. But ...
Isn't likely to be true in any meaningful sense.
Firstly, when the Andromeda and Milky Way galaxies merge, it is unlikely that any significant number of stars will collide ("significant" - say, one in a hundred thousand or more). There will be collisions between gas clouds, and a burst of star formation (including big stars with short lives and almost immediate supernovae. So the night sky is