Nav: Home

Astronomers discover new class of cosmic explosions

May 26, 2020

Astronomers have found two objects that, added to a strange object discovered in 2018, constitute a new class of cosmic explosions. The new type of explosion shares some characteristics with supernova explosions of massive stars and with the explosions that generate gamma-ray bursts (GRBs), but still has distinctive differences from each.

The saga began in June of 2018 when astronomers saw a cosmic blast with surprising characteristics and behavior. The object, dubbed AT2018cow ("The Cow"), drew worldwide attention from scientists and was studied extensively. While it shared some characteristics with supernova explosions, it differed in important aspects, particularly its unusual initial brightness and how rapidly it brightened and faded in just a few days.

In the meantime, two additional blasts -- one from 2016 and one from 2018 -- also showed unusual characteristics and were being observed and analyzed. The two new explosions are called CSS161010 (short for CRTS CSS161010 J045834-081803), in a galaxy about 500 million light-years from Earth, and ZTF18abvkwla ("The Koala"), in a galaxy about 3.4 billion light-years distant. Both were discovered by automated sky surveys (Catalina Real-time Transient Survey, All-Sky Automated Survey for Supernovae, and Zwicky Transient Facility) using visible-light telescopes to scan large areas of sky nightly.

Two teams of astronomers followed up those discoveries by observing the objects with the National Science Foundation's Karl G. Jansky Very Large Array (VLA). Both teams also used the Giant Metrewave Radio Telescope in India and the team studying CSS161010 used NASA's Chandra X-ray Observatory. Both objects gave the observers surprises.

Anna Ho, of Caltech, lead author of the study on ZTF18abvkwla, immediately noted that the object's radio emission was as bright as that from a gamma-ray burst. "When I reduced the data, I thought I had made a mistake," she said.

Deanne Coppejans, of Northwestern University, led the study on CSS161010, which found that the object had launched an "unexpected" amount of material into interstellar space at more than half the speed of light. Her Northwestern co-author Raffaella Margutti, said, "It took almost two years to figure out what we were looking at just because it was so unusual."

In both cases, the follow-up observations indicated that the objects shared features in common with AT2018cow. The scientists concluded that these events, called Fast Blue Optical Transients (FBOTs), represent, along with AT2018cow, a type of stellar explosion significantly different from others. The scientists reported their findings in papers in the Astrophysical Journal and the Astrophysical Journal Letters.

FBOTs probably begin, the astronomers said, the same way as certain supernovae and gamma-ray bursts -- when a star much more massive than the Sun explodes at the end of its "normal" atomic fusion-powered life. The differences show up in the aftermath of the initial explosion.

In the "ordinary" supernova of this type, called a core-collapse supernova, the explosion sends a spherical blast wave of material into interstellar space. If, in addition to this, a rotating disk of material briefly forms around the neutron star or black hole left after the explosion and propels narrow jets of material at nearly the speed of light outward in opposite directions, these jets can produce narrow beams of gamma rays, causing a gamma-ray burst.

The rotating disk, called an accretion disk, and the jets it produces, are called an "engine" by astronomers.

FBOTs, the astronomers concluded, also have such an engine. In their case, unlike in gamma-ray bursts, it is enshrouded by thick material. That material probably was shed by the star just before it exploded, and may have been pulled from it by a binary companion.

When the thick material near the star is struck by the blast wave, it causes the bright visible-light burst soon after the explosion that initially made these objects appear so unusual. That bright burst also is why astronomers call these blasts "fast blue optical transients." This is one of the characteristics that distinguished them from ordinary supernovae.

As the blastwave from the explosion collides with the material around the star as it travels outwards, it produces radio emission. This very bright emission was the important clue that proved that the explosion was powered by an engine.

The shroud of dense material "means that the progenitor star is different from those leading to gamma-ray bursts," Ho said. The astronomers said that in the Cow and in CSS161010, the dense material included hydrogen, something never seen in in gamma-ray bursts.

Using the W.M. Keck Observatory, the astronomers found that both CSS 161010 and ZTF18abvkwla, like the Cow, are in small, dwarf galaxies. Coppejans said that the dwarf galaxy properties "might allow some very rare evolutionary paths of stars" that lead to these distinctive explosions.

Although a common element of the FBOTs is that all three have a 'central engine,' the astronomers caution that the engine also could be the result of stars being shredded by black holes, though they consider supernova-type explosions to be the more likely candidate.

"Observations of more FBOTs and their environments will answer this question," Margutti said.

To do that, the scientists say they will need to use telescopes covering a wide range of wavelengths, as they have done with the first three objects. "While FBOTs have proven rarer and harder to find than some of us were hoping, in the radio band they're also much more luminous than we'd guessed, allowing us to provide quite comprehensive data even on events that are far away," said Daniel Perley, of the Liverpool John Moores University.
-end-
The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc. The study of CSS161010 was partially supported by the Heising-Simons Foundation, NASA, and the National Science Foundation.

National Radio Astronomy Observatory

Related Supernova Articles:

Scientists discover supernova that outshines all others
A supernova at least twice as bright and energetic, and likely much more massive than any yet recorded has been identified by an international team of astronomers, led by the University of Birmingham.
Supernova observation first of its kind using NASA satellite
Their research, detailed in the Monthly Notices of the Royal Astronomical Society, represents the first published findings about a supernova observed using TESS, and add new insights to long-held theories about the elements left behind after a white dwarf star explodes into a supernova.
Astronomers find possible elusive star behind supernova
Astronomers may have finally found a doomed star that seemed to have avoided detection before its explosive death.
Stellar thief is the surviving companion to a supernova
Hubble found the most compelling evidence that some supernovas originate in double-star systems.
Supernova may have 'burped' before exploding
Only by increasing the rate at which telescopes monitor the sky has it been possible to catch more Fast-Evolving Luminous Transients (FELTs) and begin to understand them.
An unusual white dwarf may be a supernova leftover
Astronomers have identified a white dwarf star in our galaxy that may be the leftover remains of a recently discovered type of supernova.
Researchers show how to make your own supernova
Researchers from the University of Oxford are using the largest, most intense lasers on the planet, to for the first time, show the general public how to recreate the effects of supernovae, in a laboratory.
The big star that couldn't become a supernova
For the first time in history, astronomers have been able to watch as a dying star was reborn as a black hole.
Seeing quadruple: Four images of the same supernova, a rare find
Galaxies bend light through an effect called gravitational lensing that helps astronomers peer deeper into the cosmos.
Explosive material: The making of a supernova
Pre-supernova stars may show signs of instability for months before the big explosion
More Supernova News and Supernova Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Our Relationship With Water
We need water to live. But with rising seas and so many lacking clean water – water is in crisis and so are we. This hour, TED speakers explore ideas around restoring our relationship with water. Guests on the show include legal scholar Kelsey Leonard, artist LaToya Ruby Frazier, and community organizer Colette Pichon Battle.
Now Playing: Science for the People

#568 Poker Face Psychology
Anyone who's seen pop culture depictions of poker might think statistics and math is the only way to get ahead. But no, there's psychology too. Author Maria Konnikova took her Ph.D. in psychology to the poker table, and turned out to be good. So good, she went pro in poker, and learned all about her own biases on the way. We're talking about her new book "The Biggest Bluff: How I Learned to Pay Attention, Master Myself, and Win".
Now Playing: Radiolab

Uncounted
First things first: our very own Latif Nasser has an exciting new show on Netflix. He talks to Jad about the hidden forces of the world that connect us all. Then, with an eye on the upcoming election, we take a look back: at two pieces from More Perfect Season 3 about Constitutional amendments that determine who gets to vote. Former Radiolab producer Julia Longoria takes us to Washington, D.C. The capital is at the heart of our democracy, but it's not a state, and it wasn't until the 23rd Amendment that its people got the right to vote for president. But that still left DC without full representation in Congress; D.C. sends a "non-voting delegate" to the House. Julia profiles that delegate, Congresswoman Eleanor Holmes Norton, and her unique approach to fighting for power in a virtually powerless role. Second, Radiolab producer Sarah Qari looks at a current fight to lower the US voting age to 16 that harkens back to the fight for the 26th Amendment in the 1960s. Eighteen-year-olds at the time argued that if they were old enough to be drafted to fight in the War, they were old enough to have a voice in our democracy. But what about today, when even younger Americans are finding themselves at the center of national political debates? Does it mean we should lower the voting age even further? This episode was reported and produced by Julia Longoria and Sarah Qari. Check out Latif Nasser's new Netflix show Connected here. Support Radiolab today at Radiolab.org/donate.