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Rogue stars ejected from the galaxy are found in intergalacticspace by 123wert sdfsf
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Rogue stars ejected from the galaxy are found in intergalacticspace |
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It's very difficult to knock a star out of the galaxy. In fact, themain mechanism that astronomers have come up with that can give astar the two-million-plus mile-per-hour kick it takes involvestangling with the supermassive black hole at the galaxy's core. So far astronomers have found 16 of these "hypervelocity" stars.Although they are traveling fast enough to eventually escapegalaxy's gravitational grasp, they have been discovered while theyare still inside the galaxy. Now, Vanderbilt astronomers report in a recent issue of theAstronomical Journal that they have identified a group of more than675 stars on the outskirts of the Milky Way that they argue arehypervelocity stars that have been ejected from the galactic core.
They selected these stars based on their location in intergalacticspace between the Milky Way and the nearby Andromeda galaxy and bytheir peculiar red coloration. "These stars really stand out. They are red giant stars with highmetallicity which gives them an unusual color," says AssistantProfessor Kelly Holley-Bockelmann who conducted the study withgraduate student Lauren Palladino. In astronomy and cosmology, "metallicity" is a measure of theproportion of chemical elements other than hydrogen and helium thata star contains. In this case, high metallicity is a signature that indicates aninner galactic origin: Older stars and stars from the galacticfringes tend to have lower metallicities.
The researchers identified these candidates by analyzing themillions of stars catalogued in the Sloan Digital Sky Survey. "We figured that these rogue stars must be there, outside thegalaxy, but no one had ever looked for them. So we decided to giveit a try," said Holley-Bockelmann, who is studying the behavior ofthe black hole at the center of the Milky Way galaxy. Astronomers have now found evidence for giant black holes at thecenters of many galaxies. They estimate that the Milky Way'scentral black hole has a mass of four million solar masses.
Theycalculate that the gravitational field surrounding such asupermassive black hole is strong enough to accelerate stars tohypervelocities. The typical scenario involves a binary pair of stars that getcaught in the black hole's grip. As one of the stars spirals intowards the black hole, its companion is flung outward at atremendous velocity. A second scenario takes place during periods when the central blackhole is in the process of ingesting a smaller black hole. Any starthat ventures too close to the circling pair can also get ahypervelocity kick.
Red giant stars are the end stage in the evolution of small, yellowstars like the Sun. So, the stars in Holley-Bockelmann's roguesgallery should have been small stars like the Sun when they tangledwith the central black hole. As they traveled outward, they continued to age until they reachedthe red giant stage. Even traveling at hypervelocities, it wouldtake a star about 10 million years to travel from the central hubto the spiral's edge 50,000 light years away. "Studying these rogue stars can provide us with new insights intothe history and evolution of our home galaxy," saidHolley-Bockelmann.
The researchers next step is determine if any oftheir candidates are unusually red brown dwarfs instead of redgiants. Because brown dwarfs produce a lot less light than redgiants, they would have to be much closer to appear equally bright. Heather Morrison at Case Western Reserve University, PatrickDurrell and John Feldmeier at Youngstown State University, RobinCiardullo and Richard Wade at Pennsylvania State University, and J.Davy Kirkpatrick and Patrick Lowrance at the California Instituteof California also contributed to the research, which was funded bythe National Science Foundation and the Department of Education'sGraduate Assistance in Areas of National Need fellowship. I am Construction & Real Estate writer, reports some information about purple shower curtains , plastic shower curtains.
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