2023-05-21 07:45:47
When stars like our sun die, they tend to let out a whimper rather than an explosion, 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 natureIt holds tantalizing clues about what a 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 bulge their outer layers. This process creates colorful clouds of gas erroneously called planetary nebulae and leaves behind a hot, dense and compact core called a white dwarf.
Our Sun will undergo this transformation in about 5 billion years, 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 ensuing thermonuclear explosion destroys the star in a special type of explosion called a Type Ia Supernova.
But where would the extra mass to power such an explosion come from?
We used to think it might be gas from a larger companion star in a nearby orbit. But stars tend to be messy eaters, spilling gas everywhere. A supernova explosion would shock and make any spilled gas It glows on radio waves. Despite decades of searching, no small type Ia supernova has been detected using radio telescopes.
Instead, we’re beginning to think that Type Ia supernovae must be pairs of white dwarfs spiraling inwards and merging relatively cleanly, leaving no shock gas — no radio signals.
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 like any other Type Ia supernova.
But for the next five months, it stopped fading. around the same time, Features are starting to appear Indicates the presence of abnormally rich helium gas. We are beginning to suspect that supernova 2020eyj belongs to a rare subclass of Type Ia supernovae. The shock wave, traveling at more than 10,000 kilometers per second, engulfs gas that cannot be extracted from the outer layers of a surviving companion star.
To try and confirm our hunch, we decided to test whether there was enough shocking gas present to produce a radio signal. Since the supernova is too far to the north to be observed with telescopes such as Australian Compact Telescope Array Near Narrabri, we used that instead A network of radio telescopes spread across the UK Monitoring the supernova about 20 months after the explosion.
To our surprise, we got the first clear detection of an “infant” Type Ia supernova at radio wavelengths, confirmed by a second sighting about five months later. Could it be that the “smoking gun” is that not all Type Ia supernovae are caused by the merger of two white dwarfs?
Patience pays
One of the most defining characteristics of Type Ia supernovae is that they all reach roughly the same peak in brightness. This is consistent with the fact that they all reached a similar critical mass before the explosion.
This particular feature allowed astronomer Brian Schmidt and his colleagues to investigate Nobel laureate finale At the end of the 1990s: that the expansion of the universe since the Big Bang is not slowing down due to gravity (as everyone expected), but is accelerating due to the effects of what we call today dark energy.
So Type Ia supernovae are important cosmic objects, and the fact that we still don’t know exactly how and when these stellar explosions happen, or what makes them so consistent, has astronomers worried.
In particular, if pairs of merging white dwarfs can have a total mass of nearly three times that of our Sun, why do they all release roughly the same amount of energy?
Our hypothesis (and radio confirmation) that the 2020eyj supernova occurred when enough helium gas was extracted from the companion star and onto the white dwarf’s surface to push it above mass limits, provides a natural explanation for this consistency.
The question now is why we haven’t seen this radio signal before in another 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 unexpected ways, allowing us to hear the dying whispers of a distant star.
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