A Red Supergiant Star Is Caught Going Explosively Supernova, A First

Supernova (SN) 2020tlf, identified by red markers, in the act of exploding 120 million light years away. The bright white region to the upper right is the crowded center of the star’s galaxy, the oval-shaped NGC 5731. This direct image was captured using the Pan-STARRS camera at the Haleakala Observatory, Hawai’i.  It shows the supernova in optical light. (Pan-STARRS/YSE)

When a large star reaches the end of its life it runs out of fuel, collapses and explodes into a supernova. The explosion releases enormous amounts of energy and light, turning a luminous object that is small at a distance into a large glowing ball.

Supernova temperatures have been modeled to reach 6,000 times higher than the core temperature of our Sun. Much of the matter in the star is sent flying into space and, in moments, the gigantic eruption is over. These cataclysmic events — the most energetic explosions ever seen by humans — are known to send far into the cosmos shock waves of compressed gas clouds that eventually birth new stars.

Supernova are stupendous astrophysical events which are of great interest to astronomers.  And over the past several years an international team including the University of California, Berkeley and the University of Hawai’i  have actually captured such an explosion of a red supergiant star — the first such imaging of its kind.

“For the first time, we watched a red supergiant star explode!” said Wynn Jacobson-Galán, a National Science Foundation Graduate Research Fellow at UC Berkeley and lead author of the study in The Astrophysical Journal. “This is a breakthrough in our understanding of what massive stars do moments before they die.”

“It’s like watching a ticking time bomb,” said senior author Raffaella Margutti, an associate professor of astronomy at UC Berkeley, and one of those who monitored the star for several months before it exploded.

“We’ve never confirmed such violent activity in a dying red supergiant star, where we see it produce such a luminous emission then collapse and combust. Until now.”

An artist’s video rendering of a red supergiant star transitioning into a Type II supernova, emitting a violent eruption of radiation and gas on its dying breath before collapsing and exploding.  (W. M. Keck Observatory/Adam Makarenko)

A supernova of the type and size of the one just observed are known to occur periodically,  but predicting when massive stars will reach that final violent stage and having telescopes in place to observe it has been a bridge too far.

Wynn Jacobson-Galán of UC Berkeley, and previously Northwestern University where some of this work was done, is on the international Young Supernova Experiment team, which studies cosmic explosions and other transient events. He says his research focuses on winding back the cosmic clock to understand how certain stars produce the various supernovae observed today. (UC Berkeley)

A team from an international research group called The Young Supernova Experiment (YSE), however, began watching a particular red supergiant because they had identified unusual activity on it.  YSE focuses on what are called transient events in the sky — supernova, solar flares and energy associated with the passing of asteroids and especially Near Earth Objects.

That breakthrough came in the summer of 2020,  when the continuous viewing telescope they use detected bright radiation and gas being violently ejected from the red supergiant star, which  would become SN 2020tlf.

The researchers  watched for 130 days leading up to the dramatic supernova.  It took place in the NGC 5731 galaxy and is some 120 million light-years away.

The first telescope used, the Pan-STARRS telescope on Haleakalā, Maui and operated by the Institute for Astronomy of the University of Hawaiʻi, is both a science telescope and a sentinel looking for potentially hazardous Near Earth Objects.  The telescope was funded by the U.S. Air Force.

With that early warning, the team was able to watch the star’s demise and then to capture the huge flash as it did indeed go supernova. It’s the witnessing of the process of a massive star transitioning into a supernova explosion that was the rarity.

Using the Keck Observatory on Maunakea, Hawaiʻi Island and its Low Resolution Imaging Spectrometer, they found direct evidence of dense material surrounding the star at the time of explosion — a new finding.  They concluded it was likely the same exact gas that Pan-STARRS had imaged being ejected from the red supergiant star earlier in the summer before it went supernova.

Follow-up observations of SN 2020tlf told researchers that the red supergiant star was about 10 times more massive than the Sun before its explosion.

 

After a supernova occurs, a nebula of gas and dust is generally formed from the remnant material.  This image is of a small section of the expanding remains of a massive star that exploded about 8,000 years ago to form what is called the Veil Nebula.   This view is a mosaic of six Hubble pictures of a small area roughly two light-years across, covering only a tiny fraction of the nebula’s vast structure. (NASA)

Many Worlds focuses on astrobiology — the search for life beyond Earth — and supernovae like the one just imaged are important to that study.  This is because the heavier elements essential to life are formed in stars and especially in the cauldron of a supernova implosion and then explosion.

The super-intense heat and pressure of a supernova allow the light elements of hydrogen and helium — which make up much of the universe  — to fuse together to produce new heavy elements needed for life.   The hyper-excited particles also fuse with some of the “lighter” heavy elements in the stars that were formed by their own fusion processes.

A supernova explosion not only is essential in terms of fusing elements needed for life as we know it, but they also spit all the “heavy” elements of the star out into space, and it does so as tremendous speeds.  In this way, the elements needed for life are made available across the universe.

Jacobson-Galán explained that scientists can identify the types of elements present in a supernova by examining its spectrum, which then shows atomic transitions taking place. “Red supergiants are comprised on many elements before they collapse and go supernova: lots of hydrogen, plus some helium, carbon, oxygen, silicon and iron,” he said  in an email.

“The supernova will help create other heavy elements like calcium, titanium, nickel, cobalt, barium, and scandium.”

While supernovae explosions (which come in a variety of forms based on the type and make-up of star exploding) are not often seen from Earth because of distance, interstellar dust clouds and other stars, Jacobson-Galán said they are actually quite common.

Supernovae caused by stellar core collapse,  like the one just detected,  are called Type II supernovae and he said hundreds of them are discovered each year as remnants.   He said the common rule of thumb in his field is that a supernova of some type will happen roughly ever 10 seconds somewhere in the universe.

 

Red supergiants are not only massive compared with most other stars, but they are all destined for destruction because they are the end of the evolution of certain kinds of stars.

“Not all red supergiants are as close to death as others, but every red supergiant with a mass 8 times {greater than our Sun} will explode as a supernova. Red supergiants tend to expand and increase in luminosity in their final stages of nuclear burning but they can still be tens of thousands of years away from explosion at that point.”

And that is why it was so unusual and special to find a red supergiant about to explode.

“I am most excited by all of the new ‘unknowns’ that have been unlocked by this discovery,” says Jacobson-Galán. “Detecting more events like SN 2020tlf will dramatically impact how we define the final months of stellar evolution, uniting observers and theorists in the quest to solve the mystery on how massive stars spend the final moments of their lives.”

The Young Supernova Experiment will continue hunting for the luminous radiation coming from red supergiants (and other sources) and to help solve the mystery of what massive stars do in their final moment.  The all-sky survey camera at the Vera Rubin Observatory, due for first light later this year,  is expected to help with that.

The first written evidence of a supernova comes from 185 CE , when Chinese astronomers described a “new star” resembling a “bamboo mat” that was visible in the night sky for eight months. (Most supernovae are visible for shorter periods.)

What is considered the brightest recorded supernova event star ever took place in 1006 CE.   Its presence was noted in China, the Middle East, Europe and perhaps North America. Egyptian observers reported the brightness of this star as one-quarter the brightness of the moon. Modern astronomers have discovered the faint remnant of this explosion and determined that it was only 7,100 light-years from Earth.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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