Scientists witness the birth of a new star of the Hydrogen-Poor supernova

The explosions of stars, called supernovae, can be so bright that they eclipse their host galaxies. It takes months or years to disappear, and sometimes the gaseous remains of the explosion turn into hydrogen-rich gas and become temporarily bright again – but could they stay bright without outside interference?

This is what Dan Milisavljevic, assistant professor of physics and astronomy at Purdue University, thinks has seen six years after the explosion of "SN 2012au".

"We did not see an explosion of this type on such a late time scale, unless there was an interaction with the hydrogen gas left by the star before the explosion," he said. "But there is no spectral spike of hydrogen in the data – something else has energized this thing".

As the big stars explode, their interiors collapse to a point where all their particles become neutrons. If the result neutron star has a magnetic field and rotates fast enough, it can turn into pulsar nebula of the wind.

That's probably what happened to SN 2012au, according to the results published in Astrophysical Journal Letters.

"We know that supernova explosions produce these rapidly rotating types of neutron stars, but we have never seen direct evidence at this unique moment," Milisavljevic said. "It's a key moment when the pulsar wind nebula is bright enough to act as a light bulb illuminating the outer ejectas of the explosion."

SN 2012au was already known to be extraordinary – and weird – in many ways. Although the blast was not bright enough to be described as a "superluminous" supernova, it was extremely energetic and durable, and faded into a slow luminous curve.

Milisavljevic predicts that if researchers continue to monitor extremely bright supernovae sites, they could see similar transformations.

"If there's really a pulsar nebula or magnetar in the center of the exploded star, it could push from the inside and even accelerate the gas," he said. "If we go back to some of these events a few years later and take careful measures, we could see the oxygen-rich gas moving away even faster from the explosion."

Superluminous supernovae are a hot topic in transient astronomy. They are potential sources of gravitational waves and black holes, and astronomers believe that they could be related to other types of explosions, such as gamma ray bursts and fast radio bursts. Researchers want to understand the fundamental physics that underlies them, but they are difficult to observe because they are relatively rare and arrive so far from the Earth.

Only the next generation of telescopes, which astronomers have dubbed "extremely large telescopes," will have the ability to observe these events in such detail.

"It's a fundamental process in the universe. We would not be here unless that happens, "said Milisavljevic. "Many of the essentials for life come from supernova explosions – calcium in our bones, oxygen we breathe, iron in our blood – I think it's crucial for us, citizens of the universe, to understand this. process.

Published by R. Margutti, et al., "Results of a Systematic Study of X-ray Emissions from Hydrogen-poor Superluminous SN," ApJ, 2018; doi: 10.3847 / 1538-4357 / aad2df