New sort of supernova ‘seems to be like nothing anybody has ever seen earlier than,’ astronomer says

EVANSTON, Ill. — Astronomers have noticed what they’re calling a brand new sort of supernova, which has offered an unparalleled glimpse into what occurs deep inside a star simply earlier than it explodes.

A examine detailing the shocking discovery revealed Wednesday within the journal Nature.

Massive stars are like celestial onions: The outermost layers are made up of light-weight components corresponding to hydrogen and helium whereas layers of heavier components lay beneath.

These stars, which may be 10 to 100 instances heavier than our solar, are powered by nuclear fusion, a course of during which lighter components are fused collectively to create heavier ones.

Stars start with a composition of about 75% hydrogen and 25% helium, with small quantities of carbon, nitrogen, silicon and different components, stated examine coauthor Adam Miller, assistant professor of physics and astronomy at Northwestern University.

Through fusion, which takes place on the middle of the star the place the temperature and density are the very best, hydrogen is transformed into helium to create the outer layers of the onion construction. Over a star’s lifetime, the method continues, fusing collectively lighter components to kind heavier ones and, over time, including inner layers of silicon, sulfur, oxygen, neon, magnesium, carbon beneath the helium and hydrogen.

At the very finish of the star’s life, after the entire gaseous layers have shaped, the iron core of the star kinds, Miller defined.

Fusion releases power, which produces stress that forestalls stars from collapsing in on themselves resulting from gravity, Miller stated. But when stars attempt to fuse the iron at their core into heavier components, there is not sufficient power to proceed offering stress. As a consequence, the star’s core collapses below the drive of gravity, resulting in a stellar explosion.

However, nothing went as anticipated when astronomers noticed a first-of-its-kind supernova named SN2021yfj. At some level effectively earlier than the explosion, the star had already misplaced its outer layers of hydrogen, helium and carbon. Then, simply earlier than exploding, the star launched a usually hidden layer of comparatively heavy components corresponding to silicon, sulfur and argon that aren’t typically seen in dying stars.

The star’s explosion “illuminated” the expelled layer of silicon, sulfur and argon, which had by no means been seen earlier than, Miller stated.

“This is the first time we have seen a star that was essentially stripped to the bone,” lead examine creator Steve Schulze, a analysis affiliate at Northwestern University’s Center for Interdisciplinary Exploration and Research in Astrophysics, stated in an announcement.

“It shows us how stars are structured and proves that stars can lose a lot of material before they explode. Not only can they lose their outermost layers, but they can be completely stripped all the way down and still produce a brilliant explosion that we can observe from very, very far distances.”

The discovery supplies direct proof of the long-theorized, however tough to watch, inner construction of huge stars. It can also be difficult the traditional methods during which astronomers perceive stellar evolution.

“This event quite literally looks like nothing anyone has ever seen before,” Miller stated in an announcement.

“It was almost so weird that we thought maybe we didn’t observe the correct object. This star is telling us that our ideas and theories for how stars evolve are too narrow. It’s not that our textbooks are incorrect, but they clearly do not fully capture everything produced in nature. There must be more exotic pathways for a massive star to end its life that we hadn’t considered.”

The violent life cycle of stars

The examine authors do not know precisely what sort of star existed earlier than the supernova, however they consider it had a mass about 60 instances heavier than the solar, Schulze and Miller stated. However, as a result of the outer hydrogen layer of the star had already been stripped away previous to the explosion, the star’s mass was seemingly smaller when it grew to become a supernova than when it was born, Miller added.

Massive stars have been recognized to shed outer layers of fabric earlier than exploding, however this star misplaced way more than what had been beforehand noticed. For occasion, astronomers have seen stars which were stripped of their hydrogen layer, however are nonetheless cloaked in helium, carbon and oxygen.

“Stars experience very strong instabilities,” Schulze stated. “These instabilities are so violent that they can cause the star to contract. Then, it suddenly liberates so much energy that it sheds its outermost layers. It can do this multiple times.”

In some huge star explosions, components like silicon and sulfur may be noticed “mixed” with all the opposite components as a part of the ejected materials — however they have not been seen previous to a supernova earlier than, Miller stated.

The crew estimated that the star would have wanted to launch a mass of thrice the solar over the course of its lifetime to go away behind the silicon and sulfur shell, suggesting that some stars expertise excessive losses of mass later of their lifetimes.

In this distinctive supernova, the crew noticed a thick shell of silicon and sulfur being expelled simply earlier than the star’s dying. When the star exploded, the fabric from its core collided with the gaseous shell, and the warmth of the collision triggered the silicon and sulfur layer to glow.

“This star lost most of the material that it produced throughout its lifetime,” Schulze stated. “So, we could only see the material formed during the months right before its explosion. Something very violent must have happened to cause that.”

A cosmic happenstance

The crew found the supernova in September 2021 whereas utilizing the Zwicky Transient Facility on the Palomar Observatory in Southern California. Zwicky, which scans the night time sky with a wide-field digital camera, has a fame for enabling astronomers to find transients, or fleeting cosmic phenomena, corresponding to shortly flaring and fading supernovas.

Looking over the information for proof of supernovas, Schulze seen an object that quickly elevated in brightness 2.2 billion light-years from Earth. (A single light-year is a measure of how lengthy it takes mild to journey to Earth, so the rise in brightness occurred 2.2 billion years in the past.)

To higher perceive what they have been , the crew needed to see a spectrum for the thing — wavelengths of coloured mild, with every coloration signifying a distinct ingredient. Capturing a spectrum was not attainable with Zwicky as a result of it solely measures modifications in total brightness. At first, it appeared that no different telescopes have been in a position to seize a transparent picture of the supernova. But Yi Yang, now an assistant professor at China’s Tsinghua University, noticed the thing whereas observing with the W. M. Keck Observatory in Hawaii and captured a spectrum.

Typically the seek for supernovas is finished with small telescopes that measure brightness like Zwicky, Miller stated, after which bigger telescopes like Keck are used to grasp the chemical composition of the fuel that was ejected by the explosion.

“Without that spectrum,” Miller stated, “we may have never realized that this was a strange and unusual explosion.”

The crew shared the spectrum with Avishay Gal-Yam, dean of the school of physics and professor of particle physics at Israel’s Weizmann Institute of Science. Gal-Yam, a coauthor on the examine and a number one knowledgeable in supernova science, recognized the mysterious options within the spectrum that turned out to be silicon, sulfur and argon, Schulz stated.

Stellar mysteries ensue

The crew stays not sure of what triggered the star to launch the silicon and sulfur shell and is contemplating the chance that the star interacted with a possible companion star, skilled exceptionally sturdy stellar winds or underwent an enormous pre-supernova outburst.

However, the examine authors are leaning towards the concept the star tore itself aside.

Whatever the trigger, the crew has designated its discovery as a wholly new sort of supernova referred to as a kind Ien (pronounced one-e-n) supernova, Miller stated.

Supernova classifications are based mostly on the presence of various components. Type II supernovas embody hydrogen, whereas sort Ib have helium however no hydrogen, and kind Ic have oxygen however no helium or hydrogen. Each sort of supernova exposes deeper layers of a star.

“We tend to think of massive stars forming a sequence,” Miller stated. “We call this new discovery a Ien SN because the silicon, sulfur and argon would be present only in the deepest, innermost layers of a massive star.”