For the first time, astronomers have detected a radio signal from a massive explosion of a dying white dwarf


For the first time, astronomers have detected a radio signal from a massive explosion of a dying white dwarf

This image shows some of the oldest stars in the Milky Way – ancient white dwarfs – as imaged by NASA’s Hubble Space Telescope. Image credit: NASA and H.E. Richer (University of British Columbia)

When stars like our sun die, they tend to go out loud and not explode – unless they are part of a binary (binary) star system that can lead to a supernova explosion.

Now, for the first time, astronomers have detected the radio signature of such an event in a galaxy more than 400 million light-years away. discovery, Posted May 17 in naturecarries tantalizing clues as to what the companion star might be.

The death of an exploding star

When stars up to eight times heavier than our sun begin to run out of nuclear fuel in their cores, they blow off their outer layers. This process gives rise to colorful clouds of gas known as planetary nebulae, and leaves behind a hot, dense, compact core known as a white dwarf.

Our Sun will undergo this transformation in 5 billion years or so, then slowly cool and fade. However, if the weight of a white dwarf increases in some way, the self-destruction mechanism kicks in when it becomes heavier than about 1.4 times the mass of our sun. The subsequent thermonuclear detonation destroys the star in a distinct type of explosion called a Type supernova Ia.

But where would the extra mass come from to fuel such an explosion?

We used to think it could be gas stripped from a larger companion star in nearby orbit. But stars tend to be messy eaters, spilling gas everywhere. a Supernova explosion It would shock and make any spilled gas It glows on radio waves. Despite decades of research, there is not a single young type Ia Supernova ever with radio telescopes.

Instead, we’re beginning to think that Type Ia supernovae must be pairs of white dwarfs spiraling inwards and merging together in a relatively clean way, leaving no gas for shock—and no radio signals.

For the first time, astronomers have detected a radio signal from a massive explosion of a dying white dwarf

Credit: Adam Makarenko Observatory/WM Keck, author submitted

A rare type of supernova

Supernova 2020eyj was discovered by Telescope in Hawaii on March 23, 2020. For the first seven weeks or so, it behaved quite similar to any Type Ia supernova.

But over the next five months, its brightness stopped fading. around the same time, Features are starting to appear Refers to a gas that was unusually rich in helium. We’re beginning to suspect that Supernova 2020eyj belongs to a rare subclass of Type Ia supernovae. The blast wave, traveling at more than 10,000 kilometers per second, sweeps away gas that would only have been stripped from the outer layers of a surviving companion star.

To try and confirm our hunch, we decided to test if enough gas was shocked to emit a radio signal. Since the supernova is too far to the north to be observed with telescopes such as Australia Compact Telescope Array Near Narrabri, we used that instead A group of radio telescopes spread across the UK To observe the supernova about 20 months after the explosion.

To our great surprise, we got the first ever clear detection of a “baby” Type Ia supernova at radio wavelengths, confirmed by a second observation about five months later. Could this be the “smoking gun” so that not all type Ia supernovae cause two white dwarfs to merge?

Patience pays off

One of the most distinctive characteristics of Type Ia supernovae is that they all reach roughly the same peak brightness. This is consistent with all of them reaching a similar critical mass before the explosion.

This very feature allowed astronomer Brian Schmidt and his colleagues to access them Nobel laureate finale In the late 1990s: that the expansion of the universe since the Big Bang is not slowing down under the influence of gravity (as everyone expected), but is accelerating due to the effects of what we now call dark energy.

So, Type Ia supernovae are important cosmic bodies, and the fact that we still don’t know exactly how and when these stellar explosions happen, or what makes them so consistent has been a concern for astronomers.

In particular, if there are merge pairs white dwarfs Their combined mass can be nearly three times that of our Sun, so why do they all release the same amount of energy?

Our hypothesis (and radio confirmation) that supernova 2020eyj occurred when enough helium gas was stripped from Companion star And on the white dwarf’s surface to push it above its mass limit, it provides a natural explanation for this symmetry.

The question now is why we haven’t seen this radio signal before in any other type Ia supernova. We may have tried to spot it too soon after the explosion, and gave up too easily. Or maybe not all companion stars are helium-rich and great at shedding their gaseous outer layers.

But as our study has shown, sometimes patience and perseverance pay off in ways we never expected, allowing us to hear the dying whispers of a distant star.

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