The first direct image of a star other than the Sun, made with the Hubble Space Telescope. Called … [+]
Andrea Dupree (Harvard-Smithsonian CfA), Ronald Gilliland (STScI), NASA and ESA
Betelgeuse is having moment. The famous red supergiant star in the constellation of Orion has been visibly dimming in recent weeks, leading some to ponder whether it might be about to go supernova and explode.
The last visible supernova was in 1987—Supernova 1987A—which exploded in the Large Magellanic Cloud, a satellite galaxy of our Milky Way.
Is Betelgeuse likely to explode? If so, what would it look like? Does “dimming” indicate a potential explosion is close? Or are we just being hopeful … or perhaps even looking in the wrong place?
Despite all the attention being on Betelguese, it’s almost certainly not going to explode this week and be as bright as a full moon for months on end. Meanwhile, new research suggests that the Orion constellation’s fading alpha star isn’t the only giant star to keep an eye on.
Is Betelguese about to go supernova?
That’s almost certainly not going to happen at this precise moment … but it could. Around a thousand times larger than our Sun, Betelguese is undeniably fading, but to astronomers it’s not surprising. “Far too much is being made of it by both the media and some astronomers,” says Alex Filippenko, an astrophysicist and professor of astronomy at the University of California, Berkeley. “Betelgeuse is known to be a variable star—it brightens and fades somewhat irregularly. The long-term record shows a periodic brightening and fading that’s roughly six years long and another periodicity which is roughly 400 days long … occasionally they come together and there’s a particularly low point.” That’s what’s happening now.
There are other factors at play, too. “Betelgeuse is also known to be a supergiant star whose atmosphere produces dust once in a while, which can dim the star visually as well,” says Filippenko. “All of this has been going on for hundreds or thousands of years and there’s no reason to think an explosion is imminent.”
The first direct image of a star other than our sun, taken with the Hubble Space Telescope. … [+]
Corbis via Getty Images
So when will Betelguese go supernova?
“It could be tonight, I don’t deny it,” says Filippenko. “It’s just that the current dimming is not something that’s incredibly unusual.” Estimates put Betelguese going supernova at probably within the next 100,000 years, but that’s just a best guess. “According to the most recent models it could take as long as half a million years,” says Filippenko. “It all depends on what exactly the mass of the star is and how far it’s already gone through its evolutionary burning, and we just don’t know those things for.”
An e-MERLIN image of Betelgeuse, published in the journal Monthly Notices of the Royal Astronomical … [+]
University of Manchester & e-MERLIN
If Betelgeuse does go supernova what will be see from Earth?
It’s often said that Betelgeuse could be as bright as a full moon for weeks post-supernova, but astronomers don’t actually know that for sure. “We think Betelgeuse is around 20 solar masses, but it might be as little as 15, and our observations of other such massive stars suggest that if they’re up to about 15 or 16 solar masses they explode when they’re in the red supergiant phase,” says Filippenko. “That leads to an explosion that remains about the same brightness for about three months before it stars to fade.”
However, if Betelgeuse’s mass is actually a little but more—perhaps 20 or 22 solar masses—then it could first lose much of its outer envelope of gases through a series of violent ejections. “I call them ‘cosmic burps’, and they would make the star significantly smaller when it explodes, so it would remain bright for a shorter time,” Filippenko.
This mage of the Crab Nebula taken by NASA’s Hubble Space Telescope shows the six-light-year-wide … [+]
NASA via Getty Images
What would we be left with after Betelgeuse goes supernova?
Orion the hunter’s left shoulder would be no more, though anyone with a telescope—and certainly space telescopes like Hubble and Webb—would be treated to a sight similar to a supernova remnant like the unusually bright Crab Nebula (M1) 6,500 light years distant in the constellation of Taurus. M1 is the remains of a star that went supernova in 1054, an event recorded by Chinese and Japanese astronomers. “It will depend on whether what remains on the inside is an active pulsar, a very rapidly spinning neutron star with a strong magnetic field,” says Filippenko. “Not all supernovae produce neutron stars, and not all neutron stars are highly energetic and spinning and have a very high magnetic field.”
The Crab Nebula does; its neutron star spins at a rate of about 30 or 33 times per second, resulting in a stream of energetic particles being shot out by the pulsar. “That’s what keeps the Crab Nebula energized, and makes it brighter than it would otherwise have been,” says Filippenko. “It’s what’s called a pulsar wind nebula and not all supernova remnants would be that way.” One that isn’t is Cassiopeia A (Cas A), a remnant of a supernova 11,000 light years distant in the constellation of Cassiopeia that went off in 1680, and whose neutron star is not very active.
A false color image of Cassiopeia A (Cas A) using observations from both the Hubble and Spitzer … [+]
Are there other stars that could go supernova?
“There’s no no star that we know of that is likely to go supernova any sooner than Betelguese,” says Filippenko. The exception, he explains, are so-called type 1a supernovae that can occur when two stars orbit one another, one of which is a tiny, dim white dwarf. “As one star expands at the end of its life it can dump material onto the white dwarf and in some cases its mass can grow until it gets close to about 1.4 times the Sun’s mass,” says Filippenko. In those cases an explosion can occur, though astronomers currently know little about the white dwarfs in the Milky Way (though ESA’s Gaia satellite is changing that).
“Betelgeuse is still the best bet for seeing a supernova, certainly in terms of a bright star that any person can look up and see,” says Filippenko. “Orion is quite a prominent constellation and anyone who’s familiar with it can look at his left shoulder and see that the star is noticeably dimmer than it used to be.”
The ‘nova’ predicted for the year 2083
Betelgeuse may be the closest known star that could “soon” go supernova, even if that is guessed at 100,000 years. However, some astronomers now think there’s a much closer star that could “nova”. A star called V Sagittae, 7,800 light years distant in the tiny constellation of Sagitta (just below Cygnus in the famous “Summer Triangle” asterism of stars) is barely visible even in mid-sized telescopes, but new research suggests that it could explode around the year 2083.
Although it won’t be as spectacular a sight as Betelgeuse going supernova, when V Sagittae explodes it could become as bright as Sirius, currently the brightest star visible in the night sky. It will also temporarily become the most luminous star in the Milky Way galaxy. “Around the year 2083, its accretion rate will rise catastrophically, spilling mass at incredibly high rates onto the white dwarf, with this material blazing away,” says Professor Emeritus Bradley E. Schaefer, LSU Department of Physics & Astronomy. “In the final days of this death-spiral, all of the mass from the companion star will fall onto the white dwarf, creating a super-massive wind from the merging star, appearing as bright as Sirius, possibly even as bright as Venus.”
The small constellations of Sagitta pointed up at centre and Vulpecula upper right between Albireo … [+]
Universal Images Group via Getty Images
Could V Sagittae explode sooner?
The uncertainty of the prediction is plus or minus 16 years, so it could happen between 2067 and 2099, most likely near the middle of this range. It promises to be a wonderful sight. “V Sagittae will appear startlingly bright in the night sky, said Schaefer. “This is substantially brighter than the all-time brightest known nova just over a century ago … now people the world over can know that they will see a wondrous guest star shining as the brightest in the sky for a month or so,” said Schaefer.
What is the ‘kill zone’ for supernovae? Are we safe?
Yes, we’re safe. “There’s no reason to worry about any star, certainly no nearby star, going supernova and hurting us in any way,” says Filippenko, who agrees that the “kill zone” for a supernova is somewhere in the region of 40 or 50 light-years. Betelgeuse is about 650 light years from Earth. “If Betelgeuse were to go off it would become roughly as bright as the full moon and maybe that could influence the circadian rhythms of certain animals a little bit, but it certainly wouldn’t cause an extinction,” says Filippenko. “There’s no evidence that any of the known mass extinctions in the history of life on Earth was caused by a supernova, so it’s clearly not a very common thing.”
However, he does add that there could be a threat from a supernova’s high energy radiation X-rays and gamma rays interacting with Earth’s atmosphere. “One of the primary concerns is that the ozone layer gets destroyed, which would allow much more ultraviolet radiation from the sun to come through,” says Filippenko. “That could wreak havoc, killing plankton in the ocean and affecting the entire food chain.”
Are we still hungry to see a supernova?
Wishing you clear skies and wide eyes.