Posted on May 18, 2019
A massive & # 39; ghost & # 39; the universe, believed to be one of the oldest in the universe, was seen lurking outside the Milky Way in November of 201
"It's a ghost of a galaxy," says Gabriel Torrealba, an astrophysicist at Taiwan's Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) and the leading author of the paper. "The things that are spreading as Ant 2 have not been seen before. Our discovery is only thanks to Gaia's data quality." Gaia is intrigued by the Zone of Avoidance, she says, as it provides a high quality correct motions of the stars behind the central disk of our Milky Way galaxy. That is, it is able to keep track of the stars as they move to space.
By Optically, the Zone of Avoidance is like "trying to look in a blackish black cloth," says Thomas Dame, Director of the Radio Telescope Data Center at the Harvard-Smithsonian Center for Astrophysics and Senior Radio Astronomer at the Smithsonian Astrophysical Observatory. "In terms of tracking and understanding the spiral structure, the important half of the Milky Way is terra incognito."
"This is the most important thing in astrophysics" -the & # 39; Holy Grail & # 39; of astronomy is to give a clear view of our relationship to the physical universe. The map of our Milky Way galaxy is a part of that, a map that is not yet complete. Our solar system is moving between two spiral arms on its outer edges, some 27,000 light years from its center. More than that, like ancient marine seafronts, no space has traveled beyond the unobtrusive central disk to restore and retrieve its image. "
" Monsters & Dragons? "-Mapping Terra Incognito of the Invisible Side of the Milky Way Side
"The zone of prevention is usually part of the sky covered by the Milky Way disk that is visible from Earth," says Torrealba. "The Milky Way disk has lots of gas and stars, making it so crowded and complicated." But the team got about a hundred old and poorly pulsating metal, called & # 39; RR Lyrae & # 39; stars to check inside and eventually identify Antlia 2.
By optics, entering the Zone of Avoidance is like "trying to look at a velvet-black fabric," Thomas said. Dame, Director of the Radio Telescope Data Center at the Harvard- Smithsonian Center for Astrophysics and Senior Radio Astronomers at the Smithsonian Astrophysical Observatory. "In terms of tracking and understanding the spiral structure, the important half of the Milky Way is terra incognito."
"This is the most important thing in astrophysics" -the & # 39; Holy Grail & # 39; of astronomy is to give a clear view of our relationship to the physical universe. The map of our Milky Way galaxy is a part of that, a map that is not yet complete. Our solar system is moving between two spiral arms on its outer edges, some 27,000 light years from its center. More than that, like ancient sea mariners, no vessel space had traveled beyond the opaque central disk to return and take the picture.
Drag the Faint Dwarf Galaxies Orbit the Milky Way – "More Hidden, Yet Be Discovered"
"Compared to some 60 or more Milky Way satellites, Ant 2 is an oddball," says co-author Matthew Walker, from Carnegie Mellon University. "We are wondering if this galaxy is just the tip of an iceberg, and the Milky Way is surrounded by a large population of almost unseen dwarfs like this one."
Torrealba says that Antlia 2 is equivalent to one of the oldest dwarves in the universe, but he and his colleagues are confused yet as well as how it became very diffuse. "One possibility is that Antlia 2 was much bigger in the past, and as it fell on the Milky Way, its mass lost its way to becoming more and more scattered," says Torrealba. One problem with this idea is that Torrealba is rather than grown, the galaxies are likely to diminish at the same time the stars disappear.
Discovered the Extreme Disk Galaxy – "Seven Times the Milky Way Width"
The giant size of the object, says astronomer Sergey Koposov at Carnegie Mellon University who presents the puzzle, agrees with Torrealba. "Usually, while the galaxies are lost in the mass of tides of the Milky Way, they are shrinking, not growing."
"Another possible explanation of the unusual form of Antlia 2," wrote Koposov in an email at dailygalaxy.com, "is a mistake in the current favored Cold Dark Matter theory that predicts that dark matter is should be tightly packed in the centers of the galaxies. If the dispersion of dark matter is much longer, it can make the galaxies like Antlia 2 easier, "he added.
Ant 2 is known as a dwarf galaxy. As the structures emerged in the early Universe, dwarfs were the first galaxies to develop, and so most of their stars were old, low-mass and metal-hard. But compared to other known dwarf satellites of our Galaxy, Ant 2 is immense: it's as big as the Large Magellanic Cloud (LMC), and a third the size of the Milky Way itself.
What Ant 2 does is even more unusual how easy it is to give it. Compared to the LMC, another Milky Way satellite, Ant 2 is 10,000 times. In other words, it is too big for light or too faint for its size.
The Gaia's ESA mission has made the richest star catalogs to date, with high precision measurements of nearly 1.7 billion stars and revealing previously unseen details of our Galaxy at home. Earlier in 2018, the second release of Gaia made new details of the Milky Way stars available to scientists all over the world.
Researchers behind current study – from Taiwan, UK, US, Australia and Germany – searched Gaia's new data for Milky Way satellites by using the RR Lyrae stars . These stars are old and poor metal, usually found in a dwarf galaxy. RR Lyrae changes their light with a half day and can be found thanks to these specific pulses.
"RR Lyrae found on every known dwarf satellite, so when we found a group of them sitting on top of The Galactic disc, we were not surprised enough," says co-author Vasily Belokurov from Cambridge's Astronomy Institute. "But when we looked closely at their location in the sky it was we found something new, since no one ever met something came to any of the databases we searched for."
The team interacted with Australian Anglo-Australian Telescope (AAT) colleagues, but when they checked the coordinates for Ant 2, they realized that there was a limited window of opportunity to get follow-up data. They have acquired the spectra of more than 100 red giant stars before the Earth's motion around the Sun rendered Ant 2 that has not been viewed in the months.
The spectra allowed the team to confirm that the ghostly thing they saw was true: all The stars were together. Ant 2 is not too close to the Milky Way, always staying at least 40 kiloparsecs (nearly 130,000 light-years) away. Researchers have also acquired the mass of the universe, which is less than expected for something of its size.
If the dwarf is impossible to puff up by removing the object from it, then give Ant 2 large. The team has yet to know the exact process that Ant 2 made so extended. While the matter of size and light has not been predicted in the current model of space generation, it has recently been speculated that some dwarfs can be inflated by strong formation of the star. Air stars and supernova explosions push the unused gas, which weakens the gravity that binds the universe and allows the dark matter to emerge as well.
"Although the formation of the star may redirect the dark object distribution to Ant 2 as it is together, it must act with unmatched efficiency," said co-author Jason Sanders, also from in Cambridge.
Alternatively, the low thickness of Ant 2 may mean that a change in dark matter is required. The current favored figured dark matter theory predicts to pack tightly into the centers of the galaxy. Because of how soft the new dwarf looks, a dark matter small thing that is less zealous in clusters may be required.
The gap between Ant 2 and the remaining Galactic dwarfs is immensely as it may be an indication that some important physics are missing in the dwarf space formation models. Ant 2 puzzle solving can help researchers understand how the first structures appear in the early universe.
The Daily Galaxy by Imperial College London