An enormous supernova spotted by the Gaia satellite may be the most massive ever seen by astronomers. This tremendous eruption, a billion light years from Earth, could rewrite what we know about the deaths of the largest stars in the Universe.
The star, called SN2016iet, erupted before plant or animal life had evolved on land, at a time when every continent was still huddled together into one massive supercontinent, Rodinia. Light from the event, racing toward Earth at nearly 300,000 kilometers per second (more than 186,000 miles every second), was first seen by the Gaia spacecraft on November 14, 2016.
Following three years of study, researchers have now determined this explosion was the most massive supernova ever recorded. This scale of this supernova may require physicists to rewrite the laws of physics governing these eruptions.
“When we first realized how thoroughly unusual SN2016iet is my reaction was ‘whoa — did something go horribly wrong with our data?’ After a while we determined that SN2016iet is an incredible mystery, located in a previously uncatalogued galaxy one billion light years from Earth,” states Sebastian Gomez, graduate student at Harvard University.
For millions of year before its explosion, the star shed off much of its mass, including 35 solar masses of material lost in just its final 10 years. At the time of the supernova, the dying star still possessed somewhere between 55 and 120 times as much mass as the Sun. This is created a mammoth explosion, the largest ever recorded by astronomers.
When the shock wave from the titanic explosion reached the shell of material previously cast off by the star, the impact resulted in a second shock wave which raced through the system.
Live Big, Die Young
The natural lifespan of a star is determined solely by its mass, with the most massive stars living out the shortest lives. The behemoth star which formed SN2016iet existed just a few million years before its magnificent demise. By contrast, the Sun formed roughly 4.5 billion years ago,and will shine for about the same amount of time before running out of hydrogen fuel.
The star which formed the SN2016iet supernova was a rogue star — far from its home dwarf galaxy. As SN2016iet reached the end of its life, the supermassive star shed approximately 85 percent of its mass to space over the course of a few million years. This process formed a “cocoon” of gas around the star. When the star exploded, the powerful blast from the event reached the enveloping gas, forming a second shock wave.
Telescopes at the Fred Lawrence Whipple Observatory in Amado, Arizona and the Magellan Telescopes in Chile, were engaged to study this highly-unusual supernova reported by GAIA. Everything about this stellar eruption looked bizarre.
“Everything about this supernova looks different — its change in brightness with time, its spectrum, the galaxy it is located in, and even where it’s located within its galaxy. We sometimes see supernovas that are unusual in one respect, but otherwise are normal; this one is unique in every possible way,” Edo Berger, professor of astronomy at Harvard University and co-author of a study on the discovery published in The Astrophysical Journal, states.
Astronomers studying the eruption noted vast quantities of energy released from the event over a long period of time. An unusual chemical makeup and the fact the explosion took place in a metal-poor environment all contributed to the unusual nature of this supernova. Astronomers soon realized this was a type of supernova that was first postulated decades ago, but never before seen.
This explosion was the first pair-instability supernova ever recorded. These long-theorized events occur when electron and positrons (electrons of anti-matter) temporarily reduce internal pressure, leading to runaway nuclear reactions in the core. The resulting explosion completely obliterates the star, leaving nothing behind. Usually when supernovae of this type explode, an ultra-dense neutron star or black hole is left behind. Explosions of this variety are thought to only occur in extremely massive stars living in metal-poor galaxies, like the earliest families of stars.
It All Started with a Big Bang — BANG!
When stars first formed a few hundred million years after the big bang, most were massive objects, existing in small protogalaxies. Measuring just 30 to 100 light years in diameter, these prototype galaxies would have housed vast numbers of massive stars, doomed to end their short lives in gigantic supernova explosions, like SN2016iet.
When the Universe first cooled enough for matter to exist, almost all the material that formed was hydrogen and helium (and a trace of lithium). Every element heavier than that was created in fusion reactions of stars, and everything heavier than iron came from supernova eruptions. These elements were spread to space by titanic explosions of supernovae.
All life on Earth depends on six elements — carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur. Without the elements produced by stars, life (likely) would not exist. We are truly made from stars.
“The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars. We are made of starstuff.”
― Carl Sagan, Cosmos
Data from this massive supernova could assist astronomers seeking to understand the deaths of massive stars in the ancient Universe.
Most supernovae fade after a few months, but researchers believe energy from this event will be visible for years, providing astronomers a wealth of information about this glorious, rarely-seen, class of supernovae.
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