‘Great Dimming’ of Betelgeuse star solved?
Astronomers say they’ve put to bed the mystery of why one of the most familiar stars in the night sky suddenly dimmed just over a year ago.Betelgeuse, a red supergiant in the constellation of Orion, abruptly darkened in late 2019, early 2020. The behaviour led many to speculate that it might be about to explode.
But a team using the Very Large Telescope (VLT) in Chile says the cause was almost certainly a giant dust cloud between us and the star.
Even if you can’t name many points in the sky, you’ll definitely know Betelgeuse by sight. It’s the orange dot in the top-left corner of Orion – or bottom-right, if you’re viewing the constellation in the Southern Hemisphere.
Close to Earth, relatively speaking, at a distance of about 550 light-years, Betelgeuse is what’s known as a semi-regular variable star. It naturally brightens and darkens over a period of roughly 400 days.
But what happened 18 months ago was out of the ordinary. The loss of brightness was far greater than anything previously recorded.
Image: ESO/N.Risinger (skysurvey.org)
Astronomer Miguel Montargès and colleagues investigated the event with the European Southern Observatory’s VLT, one of the most powerful telescopes on Earth. It has the resolution to directly image the surface of Betelgeuse.
The researchers compared pictures before, during and after the dimming, and did some modelling to see what kind of behaviour might give rise to the views obtained.
Two ideas were dominant. Perhaps there was a large cool spot on the surface of the star, because red supergiants like Betelgeuse are known to have very large convective cells that can cause hot spots and cold spots. Or maybe there was a cloud of dust forming right in front of the star as viewed from Earth.
The explanation turns out to be “a bit of both“, says colleague Emily Cannon from KU (Katholieke Universiteit) Leuven in Belgium.
“Our overall idea is that there was a cool spot on the star which, because of the local drop in temperature, then caused gas ejected previously to condense into dust,” she told BBC News.
“So, the cool spot on the surface would initially make the star look dimmer to us. But then this condensation of dust would add to the rapid drop in brightness of the star.“
Betelgeuse is about 15-20 times as massive as the Sun. An object that big is likely to go supernova at some point. So, it wasn’t crazy to wonder when this unusual dimming occurred that Betelgeuse might be about to let go in a spectacular explosion.
Emily Cannon said: “I don’t think this event means Betelgeuse is going to go supernova anytime soon, even though that would be incredibly interesting and I was kind of wishing it myself! We know that red supergiants can display increased mass loss rates, which may indicate there’s a later stage in their lives when they are more likely to go supernova. But Betelgeuse we think is a relatively young red supergiant and it probably has a lot more time left.”
How much time is that? Tens, even hundreds, of thousands of years is the sort of period astronomers will often quote.
It would be an amazing thing to see; the event would be visible in daylight.
The last supernova observed in our Milky Way Galaxy was Kepler’s Star, which was observed in 1604. Records from astronomers at the time indicate it was visible during the day for over three weeks.
Miguel Montargès’ team reports its findings in the journal Nature.
See more here: bbc.co.uk
PSI editor’s note: In February 1987, we witnessed what is called SN1987A, a supernova in the Large Magellanic Cloud, a dwarf satellite galaxy of the Milky Way. It occurred approximately 160,000 years ago, and was the closest observed supernova since Kepler’s Supernova in 1604.
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Tom O
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Quote –
Astronomer Miguel Montargès and colleagues investigated the event with the European Southern Observatory’s VLT, one of the most powerful telescopes on Earth. It has the resolution to directly image the surface of Betelgeuse.
The resolution to DIRECTLY image the surface of a star 550 light years away? What kind of drugs are these people on? An Earth based telescope looking up through miles of atmosphere? You can pretend all you want, but the only thing that can be “seen” is whatever their computer programs pretend they can see.
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Guido FORRIER
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[email protected]
do you know that :
The Very Large Telescope or VLT is a state-of-the-art astronomical observatory located on Mount Cerro Paranal in Chile’s Atacama Desert at an altitude of 2,635 meters. The VLT was built there so that the ESO (European Organization for Astronomical Research in the Southern Hemisphere) would experience as little hindrance as possible from clouds, light pollution and instability of the atmosphere. The sky is therefore exceptionally clear 350 nights a year.
I read to much stupide reacties here on Principia-scientific from people who think they know all about Science . When you pretend to know it : proof it with good arguments .
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T. C. Clark
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There is a technology that involves shining a laser upwards and measuring the effect of the atmosphere on the laser and then correcting for the telescope….don’t know if the VLT uses it. Stars don’t normally produce any elements beyond iron…it takes a super nova to produce elements up to plutonium.
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T. C. Clark
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The “adjustable” telescope is not a single large mirror but is divided into many smaller mirrors each computer controlled to move to compensate for the atmospheric conditions….result is remarkable.
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Herb Rose
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If the star is 15 to 20 times as large as our sun and the dimming occurs on a 400 day cycle it would seem that this large non equatorial orbiting matter is similar to an un-condensed Jupiter orbiting our sun. What if the planets are not formed at the same time as the sun, but result when enough of the larger elements are formed by the sun, it periodically ejects these heavier elements which then condense into planets?
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Jerry Krause
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Hi Herb,
These days it seems I read what is actually written very slowly. So I just have seen the relationship between your comment and what was written in the article.
This comment is to ask you: Wouldn’t a COMET’S TAIL be a DUST CLOUD as a COMET orbits this star with a fast period of only 400 days. And couldn’t we SIMPLY speculate that this star could have more comets with longer periods???
Have a good day, Jerry
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Herb Rose
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Hi Jerry,
In order to block this large sun the cloud would have to be highly dispersed.Comets, like planets, orbit in the equatorial plane of a sun so they would not cause the whole sun to dim. A comet tail is not “dust” it is matter being boiled off the main body as the energy field of the sun increases and always points away from the sun
Have a good day,
Herb
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Tom
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Wouldn’t these scientists be seeing Betelgeuse as it was 550 years ago? That is the time it takes for its light to travel to earth. How does the space dust play into the picture? Was the dust much closer to us or the star? I am not crazy about computer modeling because the outputs are limited by the input assumptions. If Betelgeuse went supernova today, we wouldn’t see it until the year 2570 or so. Hopefully, I will get a more detailed explanaion in an upcoming issue of Sky and Telescope magazine.
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Andy
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Yes you’re absolutely right Tom, we are seeing it as it was 550 years ago, that’s why I added the editor’s line at the bottom about the 1987 supernova occurring 160,000 years ago 🙂
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T. C. Clark
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Uh, Tom, Tom O sez no need to wait on Sky & Telescope….nothing there that can be seen according to him.
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