Image Credit : Wikimedia Commons
Source : CNN Indonesia
Topic: A new form of Supernova : A Prediction that turned out to be true.
Astronomers have discovered an exploding star or a new type of supernova that can provide stellar life cycles. The study, which focused on the 2018zd supernova, confirmed predictions made more than 40 years ago by astronomer Kenichi Nomoto of the University of Tokyo.
Earlier in March 2018, Japanese astronomer Koichi Itagaki observed the 2018zd supernova. He then asked astronomers to use telescopes to study it about three hours after the explosion.
This is the first time that astronomers have been able to see a star before and after a supernova.
There are two types of stellar explosions:
1) Neutron supernova
2) Thermonuclear supernova.
With the new discovery, the third type is called an electron-capturing supernova. The species was first described by Nomoto in 1980.
When the core of a star loses fuel, the force of gravity pushes away the atomic electrons and binds them to the atomic nucleus.
This sudden drop in electron pressure triggers the collapse and the star is weighed down by its own weight.
Then what is left is a dense neutron star with a mass slightly larger than the Sun.
Daiichi Hiramatsu, a graduate student at the University of California, led a team to observe and collect data on supernova 2018zd two years after the first observations.
The more data that is collected, the more researchers realize that this may be the first example of an electron-capturing supernova.
Nomoto’s theory of supernovae suggests that they carry unusual chemical signatures after the explosion, which the researchers later observed in 2018zd data.
The data also fit five other criteria in Nomoto’s theory for the proposed type of supernova.
These include strong mass loss before supernova, weak explosion, little radioactivity, nuclei rich in elements such as oxygen, neon and magnesium, and super-asymptotic branch-type stars (SAGBs). This SAGB star is an enlarged crimson giant star.
“We started by asking ‘Is this weird?’ Then we examined every aspect of SN 2018ZD and realized that everything can be explained in electron capture scenarios,” Hiramatsu was quoted as saying by CNN.
Since these stars are in a limited mass range, they are not light enough to prevent their cores from collapsing. But they are not heavy enough to produce heavy elements like iron.
“This is the most famous case for an interesting supernova category that falls between the mass limit of an exploding white dwarf and the iron core of a massive star that collapses and then bounces off and leads to an explosion, Which is called a supernova-core,” said Alex Filipenko, a professor of astronomy at the University of California.
“This study greatly improves our understanding of the late stages of stellar evolution,” he said.
Filipenko said the researchers had access to Hubble images showing the star before and after the explosion, which helped confirm the type of supernova.
According to the researchers, this type of supernova was responsible for the nebula that illuminated the sky about a thousand years ago.
Making the Crab Nebula :
Image Credit: Flickr
The result of this supernova was the famous Crab Nebula, a fascination for astronomers for many years, believed to be the result of new studies created by electron-capturing supernovae.
The brightness of the supernova is likely due to the material wasted in the explosion.
The explosion occurred when it previously collided with material released from the star, something that was also observed during the 2018zd supernova.
“I am thrilled that an electron-capturing supernova has finally been discovered, similar to what my colleagues and I predicted and related to the Crab Nebula 40 years ago,” Nomoto said in a statement.
“I really appreciate the great effort involved in getting these observations. This is an exceptional case of combining observation and theory,” Namoto said.
Astronomers will continue the search to see if they can find more examples of electron-capturing supernovae.
“This supernova has really helped us decode observations thousands of years old around the world,” said Andrew Howell, a staff scientist at the Las Cumbres Observatory and faculty member at the University of California.
“And it helps us to relate something that we don’t fully understand, the Crab Nebula, with anything else we have, this supernova,” Howell said.
In the process, Howell said, supernovae taught basic physics: how some neutron stars form, how extreme stars live and die, and how our constituent elements form and spread throughout the universe.