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A new study shows that the Milky Way has a graveyard of dead stars extending three times the height of the galaxy. Astronomers found the ancient stellar remains when they first mapped this ‘galactic underworld’.
our galaxy that Formed about 13 billion years agoIt was home to billions of stars. Over time, many of these massive objects have collapsed into dense remnants.
When a star eight times larger than the Sun burns through its elements and collapses, the star’s outer layers explode in a supernova. Meanwhile, the stellar core condenses to either become a neutron star or a black hole.
It is easy to detect modern neutron stars and black holes that formed in the Milky Way because they remain within our galaxy and conform to their shape. But the ancient stars that were in the young, evolving Milky Way were like stellar ghosts when researchers tried to find them.
The supernova explosions that collapsed stars actually pushed them into interstellar space. The researchers determined that 30% of those stellar remnants have been expelled from the galaxy altogether, according to their study published in the latest issue of the journal. Monthly Notices of the Royal Astronomical Society.
The research team was able to determine where stellar remnants survive in and around our galaxy by recreating the life cycle of ancient stars.
“One of the problems with finding these ancient objects is that until now, we had no idea where to look,” said study co-author Peter Tuthill, a professor at the School of Physics and director of the Sydney Institute for Astronomy at the University of Sydney. In Australia, in a statement.
The oldest neutron stars and black holes arose when the galaxy was younger and shaped differently, then experienced complex changes spanning billions of years. It was a big job modeling all of this to find them. It was like trying to find the legendary elephant tomb. The bones of these rare massive stars had to be present, but they seemed to obscure themselves in obscurity.”
Researchers have faced many challenges when trying to trace the steps and violent death throes of ancient stars. When a star explodes in a supernova, it receives a “kick”.
Study lead author David Sweeney, a student physician at the University of Sydney’s Sydney Institute of Astronomy, said in a statement.
Knowing the size wasn’t enough either. The team also had to model how stars and orbits they might enter would behave after a supernova experience. There was also no friction to slow down the velocity of the remnants of the stars.
“Almost all the remains that have ever formed are still there, slithering like ghosts through interstellar space,” Sweeney said.
The new map includes where stars were born within the Milky Way, where they exploded, and where they eventually rest.
Comparing the current appearance of the Milky Way to the new model of its starbursts shows striking differences. The galaxy’s distinctive spiral arms seem to disappear under all the kicks of the supernova washing away.
The “galactic underworld” also appears longer and more bulging than the Milky Way because the kicks of the supernova pushed the remnant into a kind of halo formation around the galaxy.
“It was a huge shock,” study co-author Dr Sanjib Sharma, a research fellow at the University of Sydney, said in a statement. “Every day I work with images of the galaxy visible as we know it today, and I expected the underworld of the galaxy to be very different, but similar in broad strokes. I did not expect such a drastic change in shape.”
The research team estimated that stellar ghosts might drift relatively close to our sun, astronomically speaking.
“Statistically, our closest remnant should be only 65 light-years away: roughly in our backyard, in terms of galaxies,” Tuthill said.
The map will allow scientists to identify individual remains to learn more about galactic evolution and the stellar timeline.
“Now that we know where to look, we are developing techniques to look for,” Sweeney said. “I bet the ‘galactic underworld’ won’t remain shrouded in mystery for much longer.”
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