#astronomy Superluminous Supernova, Defined? – Sky & Telescope

January 24, 2020 - Comment

Some sensible explosions not less than 10 instances extra highly effective than common supernovae may come from a white dwarf merging with an enormous companion star. However not everybody agrees on that clarification. This Hubble House Telescope picture exhibits the superluminous supernova SN 2006gy within the galaxy NGC 1260. The supernova remained sensible even 6


Some sensible explosions not less than 10 instances extra highly effective than common supernovae may come from a white dwarf merging with an enormous companion star. However not everybody agrees on that clarification.

Superluminous supernova SN 2006gy

This Hubble House Telescope picture exhibits the superluminous supernova SN 2006gy within the galaxy NGC 1260. The supernova remained sensible even 6 years after the explosion was first noticed.
NASA / HST / Fox et al. 2015

Superluminous supernovae have baffled astronomers since their discovery on the flip of the century. These sensible blasts present the traits of exploding stars, however they’re not less than 10 instances extra highly effective than common supernovae. Astronomers have invoked the dying of very large stars and even collisions between stellar behemoths as explanations.

In at the moment’s Science, Anders Jerkstrand (Max Planck Institute for Astrophysics, Germany, and Stockholm College, Sweden) and colleagues revive an outdated concept for one of the luminous supernovae ever recorded, designated SN 2006gy.

New observations, they argue, level to a reasonably easy clarification: The blast occurred when a stellar cinder generally known as a white dwarf siphoned off mass from its companion. It is a comparatively widespread approach for small stars to die, however on this case, the ensuing detonation crashed into an enormous shell of gasoline surrounding the dwarf, lighting it up in order that we might see it from 238 million light-years away.

This situation explains a lot of the observations of the occasion, together with its excessive brightness and the way in which that brightness modified over time. It might even clarify different comparable superluminous supernovae. However first it must go muster with the neighborhood, which had lengthy since eradicated the concept a low-mass star might trigger such a superb explosion.

A Large Progenitor?

Farewell Blast

Artist’s conception of a supernova
NASA / CXC / M.Weiss

After astronomers first noticed SN 2006gy outshining its whole galaxy 14 years in the past, observations confirmed that the supernova had slammed into one thing — in all probability a not too long ago ejected, large gaseous shell. This interplay left fingerprints within the occasion’s gentle spectrum that earned SN 2006gy the label “Kind IIn” — a classification it shares with a number of different (however not all) superluminous supernovae.

Most astronomers agree on this a lot. However what prompted the supernova to start with, and why did the blast comply with on the heels of an enormous ejection of mass?

Excessive-resolution photographs confirmed that the supernova had gone off close to a star-forming area. Together with different observations, this led many astronomers to suppose that the progenitor was an enormous star that had burned quick and livid earlier than it died an early dying. Nevertheless it remained unclear the place the huge shell had come from.

Iron within the FIre

Now, a brand new understanding of outdated observations casts doubt on the massive-star situation.

Jerkstrand and colleagues started by investigating a collection of unidentified emission strains seen in a spectrum taken simply over a 12 months after the supernova went off. By trawling by atomic line lists, Jerkstrand’s group was stunned to search out that the thriller strains coincided with these produced by impartial iron.

Neutral iron emission lines

Anders Jerkstrand and colleagues traced beforehand unidentified emission strains within the spectrum of SN 2006gy to the presence of impartial iron. The crimson line exhibits the noticed spectrum; the black curve exhibits the theoretical iron spectrum.
MPA

The core-collapse of an enormous star doesn’t normally depart a lot iron behind. However a Kind Ia supernova does. This explosive occasion occurs when a white dwarf, the remnant of a much less large star, eats an excessive amount of and detonates. A Kind Ia supernova can depart behind iron in portions round half the Solar’s mass. (That’s a whole lot of iron!) Based mostly on the iron emission strains in SN 2006gy’s spectrum, Jerkstrand and colleagues calculated that the occasion had produced not less than a 3rd the Solar’s mass in iron.

However Kind Ia supernovae aren’t wherever as vibrant as SN 2006gy was. A detonating white dwarf would have needed to convert nearly all of its power into radiation to provide that a lot gentle. That may occur, Jerkstrand explains, if the explosion slams right into a shell that’s far more large than the exploding dwarf itself.

So, right here’s what the group proposes:

Because the white dwarf was siphoning mass off of its big companion star, the 2 stars spiraled towards one another. They got here so shut, in truth, that they shared a standard envelope, mainly buying and selling gasoline between them. However that envelope wasn’t secure. As the celebs continued to spiral inward, the widespread envelope was ejected so­me 10 to 200 years earlier than the stellar cores merged and exploded. This situation explains the connection between the mass ejection and the supernova itself.

Passing Muster

However not all people finds this connection convincing.

“I’m skeptical,” says Stan Woosley (College of California, Santa Cruz). “There is no such thing as a apparent motive that the merger of a white dwarf with the core of a large star would make the white dwarf explode.” For instance, he provides, the additional materials falling onto the white dwarf because it spirals into the large star might have ignited “mild burning” that proceeds from the floor inward. Such a detonation would have been extra contained.

Jerkstrand and his colleagues acknowledge that their situation hasn’t been explored a lot in simulations. The ball, in different phrases, is within the theorists’ courtroom.

Woosley additionally notes that it’s troublesome to exactly estimate the quantity of iron current primarily based on spectra taken so lengthy after the supernova went off. But when the iron measurement pans out, it is going to be essential for understanding what occurred to create the blast.

One fashionable situation, which Woosley calls “considered one of my favourite fashions,” is a pulsational pair instability, whereby a star with the mass of 100 Suns explosively ejects big quantities of its outer envelope. “If any new iron had been current,” Woosley says, “it might rule towards a pulsational pair instability supernova origin.”

Whereas a number of different superluminous supernovae might additionally match by the situation described by Jerkstrand’s group, it is going to be troublesome to inform — they’re all farther away and if iron has left fingerprints of their spectra, the imprints can’t be seen.



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