Astronomers have discovered a new way that stars can die.
In a study published in the journal Nature Astronomy, experts have worked out that a minute-long gamma-ray burst of light, which occured in 2019 and evidence a star dying, happened because stars collided within the densely crowded environment near the supermassive black hole at the centre of an ancient galaxy.
Normally gamma-ray bursts (GRB) last around two seconds and happen when stars collapse.
“For every hundred events that fit into the traditional classification scheme of gamma-ray bursts, there is at least one oddball that throws us for a loop,” said study coauthor Wen-fai Fong, assistant professor of physics and astronomy at Northwestern University’s Weinberg College of Arts and Sciences, in a statement. “However, it is these oddballs that tell us the most about the spectacular diversity of explosions that the universe is capable of.”
Over time, astronomers have observed three main ways that stars can die, depending on their size. Lower mass stars like our sun shed their outer layers as they age, eventually becoming dead white dwarf stars.
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Massive stars burn through the fuel-like elements at their core and shatter in explosions called supernovas. Doing so can leave behind dense remnants like neutron stars or result in the creation of black holes.
A third form of star death results when neutron stars or black holes begin to orbit one another in a binary system and spiral closer to one another until they collide and explode.
But the new observation suggests a fourth type of death. “Our results show that stars can meet their demise in some of the densest regions of the universe, where they can be driven to collide,” said lead study author Andrew Levan, an astrophysics professor at Radboud University in Nijmegen, Netherlands, in a statement. “This is exciting for understanding how stars die and for answering other questions, such as what unexpected sources might create gravitational waves that we could detect on Earth.”
“The lack of a supernova accompanying the long GRB 191019A tells us that this burst is not a typical massive star collapse,” said study coauthor Jillian Rastinejad, a doctoral student of astronomy at Northwestern, in a statement. “The location of GRB 191019A, embedded in the nucleus of the host galaxy, teases a predicted but not yet evidenced theory for how gravitational-wave emitting sources might form.”
“While this event is the first of its kind to be discovered, it’s possible there are more out there that are hidden by the large amounts of dust close to their galaxies,” said Fong, who is also a member of the Center for Interdisciplinary Exploration and Research in Astrophysics at Northwestern. “Indeed, if this long-duration event came from merging compact objects, it contributes to the growing population of GRBs that defies our traditional classifications.”
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