Total annihilation for supermassive stars

Total annihilation for supermassive stars
Artist’s concept of the SN 2016iet pair-instability supernova. Illustration by Joy Pollard. Credit: Gemini Observatory/NSF/AURA/

A renegade star exploding in a distant galaxy has forced astronomers to set aside decades of research and focus on a new breed of supernova that can utterly annihilate its parent star—leaving no remnant behind. The signature event, something astronomers had never witnessed before, may represent the way in which the most massive stars in the Universe, including the first stars, die.

The European Space Agency's (ESA) Gaia satellite first noticed the supernova, known as SN 2016iet, on November 14, 2016. Three years of intensive follow-up observations with a variety of telescopes, including the Gemini North telescope and its Multi-Object Spectrograph on Maunakea in Hawaiʻi, provided crucial perspectives on the object's distance and composition.

"The Gemini data provided a deeper look at the supernova than any of our other observations," said Edo Berger of the Harvard-Smithsonian Center for Astrophysics and a member of the investigation's team. "This allowed us to study SN 2016iet more than 800 days after its discovery, when it had dimmed to one-hundredth of its peak brightness."

Chris Davis, program director at the National Science Foundation (NSF), one of Gemini's sponsoring agencies, added, "These remarkable Gemini observations demonstrate the importance of studying the ever-changing Universe. Searching the skies for sudden explosive events, quickly observing them and, just as importantly, being able to monitor them over days, weeks, months, and sometimes even years is critical to getting the whole picture. In just a few years, NSF's Large Synoptic Survey Telescope will uncover thousands of these events, and Gemini is well positioned to do the crucial follow-up work."

In this case, this deep look revealed only weak hydrogen emission at the location of the supernova, evidence that the progenitor star of SN 2016iet lived in an isolated region with very little star formation. This is an unusual environment for such a massive star. "Despite looking for decades at thousands of supernovae," Berger resumed, "this one looks different than anything we have ever seen before. We sometimes see supernovae that are unusual in one respect, but otherwise are normal; this one is unique in every possible way."

SN 2016iet has a multitude of oddities, including its incredibly long duration, large energy, unusual chemical fingerprints, and environment poor in heavier elements—for which no obvious analogues exist in the astronomical literature.

"When we first realized how thoroughly unusual SN 2016iet is, my reaction was 'Whoa—did something go horribly wrong with our data?'" said Sebastian Gomez, also of the Center for Astrophysics and lead author of the investigation. The research is published in the August 15th issue of The Astrophysical Journal.

Total annihilation for supermassive stars
Image of SN 2016iet and its most likely host galaxy taken with the Low Dispersion Survey Spectrograph on the Magellan Clay 6.5-m telescope at Las Campanas Observatory in i-band on July 9, 2018. Credit: GEMINI Observatory

The unusual nature of SN 2016iet, as revealed by Gemini and other data, suggest that it began its life as a star with about 200 times the mass of our Sun—making it one of the most massive and powerful single star explosions ever observed. Growing evidence suggests the first born in the Universe may have been just as massive. Astronomers predicted that if such behemoths retain their mass throughout their brief life (a few million years), they will die as pair-instability supernovae, which gets its name from matter-antimatter pairs formed in the explosion.

Most massive stars end their lives in an explosive event that spews matter rich in into space, while their core collapses into a neutron star or black hole. But pair-instability supernovae are a different breed. The collapsing core produces copious gamma-ray radiation, leading to a runaway production of particle and antiparticle pairs that eventually trigger a catastrophic thermonuclear explosion that annihilates the entire star, including the core.

Models of pair-instability supernovae predict they will occur in environments poor in metals (astronomer's term for elements heavier than hydrogen and helium), such as dwarf galaxies and the early Universe—and the team's investigation found just that. The event occurred at a distance of one billion light years in a previously uncatalogued dwarf galaxy poor in metals. "This is the first supernova in which the mass and metal content of the exploding star are in the range predicted by theoretical models," Gomez said.

Another surprising feature is SN 2016iet's stark location. Most are born in dense clusters of stars, but SN 2016iet formed in isolation some 54,000 away from the center of its dwarf host galaxy.

"How such a massive star can form in complete isolation is still a mystery," said Gomez. "In our local cosmic neighborhood, we only know of a few stars that approach the mass of the star that exploded in SN 2016iet, but all of those live in massive clusters with thousands of other stars." To explain the event's long duration and slow brightness evolution, the team advances the idea that the progenitor star ejected matter into its surrounding environment at a rate of about three times the mass of the Sun per year for a decade before the star blew itself into oblivion. When the star ultimately exploded, the supernova debris collided with this material powering SN 2016iet's emission.

"Most supernovae fade away and become invisible against the glare of their host galaxies within a few months. But because SN 2016iet is so bright and so isolated we can study its evolution for years to come," said Gomez. "The idea of pair-instability supernovae has been around for decades," said Berger. "But finally having the first observational example that puts a dying star in the right regime of mass, with the right behavior, and in a metal-poor dwarf galaxy is an incredible step forward."

Not long ago, it was not known if such supermassive stars could actually exist. The discovery and follow-up observations of SN 2016iet have provided clear evidence for their existence and potential for affecting the development of the early Universe. "Gemini's role in this amazing discovery is significant," said Gomez, "as it helps us to better understand how the early Universe developed after its 'dark ages'—when no star formation occurred—to form the splendor of the Universe we see today."

Explore further

Modeling a core collapse supernova

More information: Sebastian Gomez et al. SN 2016iet: The Pulsational or Pair Instability Explosion of a Low-metallicity Massive CO Core Embedded in a Dense Hydrogen-poor Circumstellar Medium, The Astrophysical Journal (2019). DOI: 10.3847/1538-4357/ab2f92 ,
Journal information: Astrophysical Journal

Provided by Gemini Observatory
Citation: Total annihilation for supermassive stars (2019, August 15) retrieved 17 September 2019 from
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User comments

Aug 15, 2019
Why does our world have a particular non-zero baryonic number? The term "asymmetry of baryogenesis" does not explain anything; this is simply a statement of fact. The availability of the energy is a necessary but not sufficient condition. The method of creation of the matter, our universe consists of, was different than that in accelerators. The space and its evolution are the primary sources of phenomena in Mega- and micro-worlds. Thus cosmology and particle physics have the same active agent - physical space.

Aug 16, 2019
I would have liked the article to cite the researchers certainty of distance. All they seem to have is a smudge of pixels and a lack of data culled from one observatory. Hardly compelling evidence

Aug 16, 2019
I would have liked the article to cite the researchers certainty of distance. All they seem to have is a smudge of pixels and a lack of data culled from one observatory. Hardly compelling evidence

Can you even read?

"Three years of intensive follow-up observations with a variety of telescopes, including the Gemini North telescope and its Multi-Object Spectrograph on Maunakea in Hawaiʻi, provided crucial perspectives on the object's distance and composition"

Aug 16, 2019
This comment has been removed by a moderator.

Aug 16, 2019
Fine, from a 'few' observatories. I had to go to another article and the original press release for the details. This article sucks and your attitude stinks. Fuck you.

Usually it's good to read the original paper before dissing it. Fuck me indeed.

Aug 16, 2019
Another anti-science troll to block. Yay.

Aug 16, 2019
Meanwhile, this is a pretty important discovery for stellar evolution knowledge. Early times stellar formation models can now be tweaked, and this will lead to better galaxy formation models.

Aug 16, 2019
Antimatter Supernova in Annihilation - pair-instability supernova

A Supernova star
Has forced astronomers
To set aside decades of research
focus on a Supernova
That utterly annihilates its parent star
Leaving no remnant behind

SN 2016iet
began its life as a star
With 200 times the mass of our Sun
One of the most massive
Creating the most powerful single star explosions ever observed

Supernova SN 2016iet
Is described by the researchers
In The Astrophysical Journal
As a pair-instability supernova!
The outer layer collapses with such energy
Those gamma rays are produced
Which turn into pairs of electrons and positrons
The matter and antimatter production
From the gamma rays
Propagates through the entire star
Pairs of particle-antiparticles
Continue to form
Annihilate the Star

Aug 17, 2019
Pair-instability supernova

Pair-instability supernova
Occur when pair production of free electrons and positrons
In the collision between atomic nuclei and energetic gamma rays
Reduces the internal pressure supporting a supermassive star's core against gravitational collapse
This pressure drop leads to a partial collapse
Causing accelerated burning
In a runaway explosion
Resulting in the star being blown completely apart
Without leaving a black hole remnant behind
Pair-instability supernovae can only happen in stars
From 130 to 250 solar masses

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