Astronomers decode Milky Way's violent birth

The Milky Way contains at least 100 billion stars and its centre contains an intense radio source believed to be the supermassiv
The Milky Way contains at least 100 billion stars and its centre contains an intense radio source believed to be the supermassive black hole Sagittarius A

The Milky Way gobbled up a galaxy one quarter of its mass 10 billion years ago in a "violent collision" that didn't fully settle for eons, astronomers said in new research published Monday.

Previous studies had suggested that our home galaxy was composed of two separate sets of stars, but the precise chronology of the galactic merge remained elusive.

Researchers from the Instituto de Astrofisica de Canarias (IAC) used the Gaia space telescope to take exact measurements of the position, brightness and distance of around one million stars in the Milky Way within 6,500 light years of the Sun.

They identified two distinct stellar sets—one "bluer" and containing less metal, one "redder" containing more.

After studying their movement and composition, the team determined that both sets of stars were equally old, but the bluer ones had been set into a "chaotic motion"—evidence of the Milky Way swallowing a smaller galaxy in the distant recesses of time.

"The novelty of our work is that we have been able to assign precise ages to the stars that belong to the that merged and, by knowing these ages, when the merger took place," Carme Gallart, lead author of the study published in Nature Astronomy, told AFP.

She said the collision, around 10 billion years ago, would have taken millions of years to unfold.

"It's a very gradual process—it's not something like a car crash—it's something that has an effect on the galaxy as a whole. It's very massive so it happens slowly in human terms, not so slowly in cosmic time."

The team believes remnants of the dwarf galaxy, known as Gaia-Enceladus, eventually formed the halo of the present-day Milky Way.

They also determined that the collision contributed to "violent bursts" of for around another four billion years, after which gas from those formations settled into the Milky Way's thin disk that runs through the centre of the galaxy.

The Milky Way contains at least 100 billion and its centre contains an intense radio source believed to be the supermassive black hole Sagittarius A*.


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A massive collision in the Milky Way's past

More information: Uncovering the birth of the Milky Way through accurate stellar ages with Gaia, Nature Astronomy (2019). DOI: 10.1038/s41550-019-0829-5
Journal information: Nature Astronomy

© 2019 AFP

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Jul 22, 2019
"The team believes remnants of the dwarf galaxy, known as Gaia-Enceladus, eventually formed the halo of the present-day Milky Way."

Obviously, it is that "halo" that was derived from a small galaxy's collision with our Milky Way, that Dark Matter cultists think is their Dark Matter woo.

Such collisions between big galaxies and little ones may have occurred many times in the past, and the smaller galaxies spread out to form other "halo" also. Thus, the only 'Dark Matter' in the Universe must be thinly spread-out galaxies that surround larger ones in the form of a halo. No Dark Matter faerie dust.

Jul 22, 2019
So jebus did it?

Uh huh.

Thanks Moe.

Jul 22, 2019
Milky Way is a pretty calm galaxy with low star formation rate, c.f. how comparably massive Andromeda has several times more stars. From the conclusion:

"This merger heated some of the existing stars in the main progenitor into a stellar halo-like configuration. A ready supply of infalling gas during the merger ensured the maintenance of a disk-like configuration, with the thick disk continuing to form stars at a substantial rate. Subsequently, around 8–6 Gyr ago, the gas settled into a thin disk that has continued to form stars until the present day."

Seems that aside from this early and large merger, the Milky Way has been mostly assimilating smaller galaxies like the Magellanic Clouds (IIRC Gaia has founds 10s or 100s of merger remnants inside the halo). Just a lonely wanderer, which may be why we find ourselves here (i.e. in calm waters) instead of in a larger galaxy - survival bias.

@DS: Someone lying-for-jebus again? How 'surprising'.

Jul 22, 2019
I checked, and consistent with survival bias - if that is the reason we live here - Sun is a late thin disk star [ https://en.wikipe...hin_disk ]. (That image is old BTW, AFAIK Gaia & DM models says MW is larger and Sun is half way out.)

Jul 22, 2019
Watch out @torbjorn, they'll be whining about the anthropic principle and stuff.

Jul 22, 2019
God spoke the universe into existence less than 7000 years ago...what science
is looking for does not exist. The solar system is young..still active and planet
earth is a water world...as it was formed from water.

Jul 22, 2019
There are some very complicated issues of galaxy formation. Unfortunately, here is the same problem as with the stars. The origin of galaxies remains unclear, in spite of huge activity in the field. What the "formation" means? It means that we have the material that is assembling into galaxies.
https://www.acade...ome_From

Jul 22, 2019
"The team


you're quite a strange little fellow.

Jul 22, 2019
"The team believes remnants of the dwarf galaxy, known as Gaia-Enceladus, eventually formed the halo of the present-day Milky Way."

Obviously, it is that "halo" that was derived from a small galaxy's collision with our Milky Way, that Dark Matter cultists think is their Dark Matter woo.

Such collisions between big galaxies and little ones may have occurred many times in the past, and the smaller galaxies spread out to form other "halo" also. Thus, the only 'Dark Matter' in the Universe must be thinly spread-out galaxies that surround larger ones in the form of a halo. No Dark Matter faerie dust.

How did Bohr say it? "This is not even wrong"
The "halo" referred to in the article is NOT the dark matter halo extending half a million light years into space around the Milky Way.
There is a halo around the core of the Milky Way about a couple thousand light years across where the stars form a sphere instead of a flat disk. Real stars, real matter, nothing mysterious or magic.

Jul 23, 2019
This topic is like some surmising that somehow the moon was formed in a violent collision. The physics just doesn't work. As terms of galaxies colliding, the physics here is also just not present. No one can even come close as to explain how all of the stars fall into place and rotate in the same direction, even after billions of years. If you can explain that somehow, you would be given the nobel prize. But it is impossible.

Jul 23, 2019
"The team


you're quite a strange little fellow.
says Shootist

For your further edification, that is part of a quote that I copied from the article above.

Jul 23, 2019
"The team believes remnants of the dwarf galaxy, known as Gaia-Enceladus, eventually formed the halo of the present-day Milky Way."

Obviously, it is that "halo" that was derived from a small galaxy's collision with our Milky Way, that...

Such collisions between big galaxies and little ones may have occurred many times in the past, and the smaller galaxies spread out to form other "halo" also. Thus, the only 'Dark Matter' in the Universe must be thinly spread-out galaxies that surround larger ones in the form of a halo. No Dark Matter faerie dust.


The "halo" referred to in the article is NOT the dark matter halo extending half a million light years into space around the Milky Way.
There is a halo around the core of the Milky Way about a couple thousand light years across where the stars form a sphere instead of a flat disk. Real stars, real matter, nothing mysterious or magic.


No matter how many halo there are, they are still not Dark Matter.

Jul 23, 2019
@Scientologist_Egg_Unit hates dark matter because it's not Xenu.

Jul 23, 2019
like i endlessly repetition
i it is the poor choices of simplistic words by scientists to popularize what are essentially complex phenomena

& every time they get the woolooneyticks all stirred up
too pestering every body else with their ravings

the use of the word "halo" os a good example of how the simple-minded apply their stuporstitious nonsense to scientific terms

some scientific comedian will want to use the words "wings" & "robes" next
to describe extraneous random distribution of galactic dust-bunnies

okay, i can understand the grandiose fetish of halos
but
why do angels need robes?
wouldn't that contradict the concept of shame?
& wouldn't those be interfering with the wings?
& why wings in the heavens?
wouldn't rockets work better?

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