Astronomers propose method for predicting the stars that will go supernovae

The uncertainty of science: Using a computer model based on the most recent data that suggests red supergiant stars like Betelgeuse are the kind of stars that produce certain kinds of supernovae, astronomers now think they have a method for predicting which of those stars are about to go supernovae.

You can read the science paper here. From the link above:

In a few examples, astronomers have looked back at old catalogs and found images of the stars before they exploded, and they all seem to be red supergiants like Betelgeuse. That’s a clear indication that those kinds of stars are supernova candidates, ready to go off at a moment’s notice.

The stars that result in these kinds of supernovas are thought to have dense shrouds of material surrounding them before they explode. These shrouds are orders of magnitude denser than what’s measured around Betelgeuse.

More importantly, the data suggests that once this shroud of material forms, the supernova will follow, in just a few years. As the scientists conclude in their paper:

The final overarching conclusion we can make from this work is that, shortly before core-collapse, [red supergiants] must undergo some prodigious mass-losing event which radically alters the appearance of the star. Therefore, the signature of an imminent explosion should be a dramatic change in the progenitor stars’ optical – near-IR photometry on timescales of less than a month. Such a signature should be detectable in the coming era of wide-field short cadence photometry. [emphasis mine]

Near-IR (infrared) photometry is exactly in the wavelengths in which the James Webb Space Telescope operates. Thus, if it is lucky and sees this kind of star in an image, and a supernova follows shortly thereafter, this theory will have been proven correct.

Astronomers used Japanese weather satellite to monitor the dimming of Betelgeuse

Belelgeuse as seen by weather satellite
From Figure 1 of the paper. Click for full image and caption.

In a paper published on May 30th, astronomers described how they used the Japanese weather satellite Himawari-8 to monitor the dimming of Betelgeuse that occurred in 2019 and 2020.

“We saw a tweet stating that the moon was in its images,” Daisuke Taniguchi, a Ph.D. student in astronomy at the University of Tokyo and first author of the paper, told “I chatted with [third author] Shinsuke Uno on the usage of meteorological satellites for astronomy, found Betelgeuse is in the field of view of Himawari-8 and realized that maybe the Great Dimming of Betelgeuse could be investigated.”

Himawari-8 has been positioned 22,236 miles (35,786 kilometers) above Earth’s equator since 2015 to study weather and natural disasters (including the eruption of the Hunga Tonga-Hunga Haʻapai volcano on Jan. 15). Although the satellite is up there to image Earth every 10 minutes, the edges of its images include stars.

Taniguchi and his colleagues were able to see Betelgeuse in images taken throughout Himawari-8’s lifetime and measured its brightness roughly every 1.7 days between January 2017 and June 2021.

The scientists were lucky that the star’s unexpected dimming happened to occur during this time period. The image above is Figure 1 from their paper (which you can read here).

They note that their observations appeared to confirm the theory that the dimming was caused by a dust cloud crossing in front of the star, not the theory that it was caused by a dark spot on the star’s surface. Moreover, their data suggests that dust was relatively close to the star, and could even been created by a burst from the star.

Scientists: Betelgeuse dimmed because of giant dark spot on surface

The uncertainty of science: A new study by scientists in China now proposes that the dimming of the red giant star Betelgeuse in 2019-2020 was because of a giant dark and cold spot on its surface.

When Betelgeuse was at its dimmest on Jan. 31, 2020, its effective temperature — meaning, the temperature calculated from its emitted radiation — was measured at 3,476 degrees Kelvin (about 5,800 degrees Fahrenheit or 3,200 degrees Celsius.)

But once the star was back to a normal luminosity, measurements indicated an almost 5% temperature rise to 3,646 Kelvin (roughly 6,100 F or 3,370 degrees C.)

…[T]he astronomers … concluded it is unlikely the entire surface cooled temporarily by that amount. Rather, it must have been a sunspot — or rather, a “star spot” — blocking some of Betelgeuse’s radiation from escaping, they said.

This new hypothesis aligns partly with others that say it was a combination of a dark spot and intevening dust that caused the dimming.

None of these hypotheses however “solve” the mystery. Too little concrete information exists at present to do that.

Astronomers propose explanation the dimming of Betelgeuse in 2020

The uncertainty of science: New data has allowed astronomers to propose a more detailed explanation for the dimming of Betelgeuse in 2020 by almost two-thirds.

[T]he dimming was likely to be caused by [one of two] mechanisms, such as a blob of unusually cold matter appearing on the surface of the star in what’s known as a convective cell, or a cloud of dust crossing the line of sight to it.

Now, astrophysicist Miguel Montargès at the Paris Observatory and his collaborators have found that the reason for the ‘great dimming’ was probably a combination of both of those factors

The data suggest that the star spewed out material from a convection cell, which then quickly condensed into dust which acted to block the star’s light. The growing cell itself also was darker, which also contributed to the dimming.

The results, while robust, are still uncertain. While a number of mainstream news sources are claiming the mystery of Betelgeuse’s dimming has been “solved”, that is not how it works. The data now points to an answer, but the data is far from complete, and future observations could very easily change that answer.

Betelgeuse is closer and smaller than previously thought

Betelgeuse's fading
Images taken by Europe’s
Very Large Telescope in Chile

The uncertainty of science: A new analysis by scientists of Betelgeuse, triggered by its dip in brightness in 2020, has concluded that the red giant star is both closer and smaller than previously estimated.

Their analysis reported a present-day mass of 16.5 to 19 solar mass—which is slightly lower than the most recent estimates. The study also revealed how big Betelgeuse is, as well as its distance from Earth. The star’s actual size has been a bit of a mystery: earlier studies, for instance, suggested it could be bigger than the orbit of Jupiter. However, the team’s results showed Betelgeuse only extends out to two-thirds of that, with a radius 750 times the radius of the sun. Once the physical size of the star is known, it will be possible to determine its distance from Earth. Thus far, the team’s results show it is a mere 530 light years from us, or 25 percent closer than previously thought.

The research also suggested that the star is in the initial stages of burning helium rather than hydrogen, and so it likely more than 100,000 years from going supernova.

As for the dimming, the scientists concluded (as other have) that the dimming in ’20 was due to the passage of a dust cloud in front of the star.

Betelgeuse dimming caused by outburst

The uncertainty of science: According to new data from the Hubble Space Telescope, astronomers are now proposing that the dimming seen earlier this year in the red giant Betelgeuse was caused not by a known variation cycle or by a large starspot moving across its surface, but by an large outburst of material, thrown out from the star.

Ultraviolet observations by the Hubble Space Telescope suggest that the unexpected dimming was probably caused by an immense amount of superhot material ejected into space. The material cooled and formed a dust cloud that blocked the starlight coming from about a quarter of Betelgeuse’s surface.

That we now have three creditable but different theories, all based on evidence, for explaining the dimming that occurred from October 2019 to April 2020 suggests that we really still have no idea what specifically caused it. All three theories however are based on what we do know about Betelgeuse, that it is giant blobby gasbag that has dark starspots on its surface, that has giant convection cells that bubble up from below and release material periodically, and that it pulses in a variety of cycles predictably over time.

It could be any of these phenomenon that caused last year’s dimming, or even a combination of two or more. The information available so far is just too sketchy to pin this down more precisely.

Giant dark starspots explain Betelgeuse’s dimming last year

Astronomers now think that unusually large dark starspots on the face of the red supergiant star Betelgeuse caused its dimming from October 2019 to April 2020.

“Corresponding high-resolution images of Betelgeuse from December 2019 show areas of varying brightness. Together with our result, this is a clear indication of huge star spots covering between 50% and 70% of the visible surface and having a lower temperature than the brighter photosphere,” said co-author Peter Scicluna from the European Southern Observatory (Eso).

“For comparison, a typical sunspot is the size of the Earth. The Betelgeuse star spot would be a hundred times larger than the Sun. The sudden fading of Betelgeuse does not mean it is going supernova. It is a supergiant star growing a super-sized star spot.” said co-author Prof Albert Zijlstra from The University of Manchester, UK

Starspots have been identified on the surface of Betelgeuse previously, so what is interesting here is how large these spots were.

Images reveal changes in Betelgeuse’s shape as it has been dimming

Betelgeuse dimmed
Click for full image.

Using the Very Large Telescope in Chile astronomers have produced before and after images of the red giant Betelgeuse, showing the changes to the star in the past year as it has dimmed by about 36%.

The image to the right, cropped and reduced to post here, was taken in December and shows the star in its dimmed state. Below the fold is a short video that compares this image with a photograph taken in January 2019. The star was then more spherical and evenly bright.

Betelgeuse’s misshaped profile and uneven brightness is not actually a new thing. See for example this 2017 image, where I noted that the bulge on the star’s side suggested “that continuous observations would reveal the outer atmosphere waxing and waning almost like the stuff inside a lava lamp.” The star is a giant gasbag that in the past has frequently been observed with dark patches on its surface and a sense that it is not always spherical. Those changes however have not occurred with such a significant dimming, a full magnitude

In late December I had posted a story noting that the dimming appeared to be expected, caused by the alignment of two different regular fluctuations of brightness, one 5.9 years long and the other 0.5 year long. It was expected that the star would begin brightening again.

Right now astronomers estimate that the low point in these cycles will occur on approximately February 21st. If the star begins to brighten following that date it would confirm that this dimming is just part of its cycles. If not, then it could be that we are in the preliminaries to a supernova event that would probably make Betelgeuse bright enough to be seen during the day.
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Astronomers take best image of Betelgeuse yet


Using the Atacama Large Millimeter/submillimeter Array Telescope (ALMA), astronomers have produced the best picture of the red giant star Betelgeuse taken so far.

Using ESO’s Very Large Telescope astronomers discovered a vast plume of gas almost as large as our Solar System. Astronomers have also found a gigantic bubble that boils away on Betelgeuse’s surface. These features help to explain how the star is shedding gas and dust at tremendous rates (eso0927, eso1121). In this picture, ALMA observes the hot gas of the lower chromosphere of Betelgeuse at sub-millimeter wavelengths — where localised increased temperatures explain why it is not symmetric.

The image on the right is that image, slightly reduced to post here. The bulge on the star’s left illustrates the unevenness of the star’s upper atmosphere. I suspect that continuous observations would reveal the outer atmosphere waxing and waning almost like the stuff inside a lava lamp.

Betelgeuse might have eaten a star

Because the red giant star Betelgeuse rotates far faster than it should, astronomers are now theorizing that when it expanded into its present red giant phase about 100,000 years ago it swallowed a companion star which contributed its own angular momentum to the system to speed up the rotation.

This theory is bolstered by evidence of a shell of matter surrounding Betelgeuse that is possibly a remnant of that destroyed star.

Betelgeuse baffles astronomers

The uncertainty of science: New data of the red giant star Betelgeuse says that the star simply doesn’t have the energy to eject the large amount of gas it routinely blows into space.

“[W]e now have a problem”, says Graham Harper, an astrophysicist at the University of Colorado Boulder. “If you’re going to eject matter you have to put energy in, and we’re not seeing that.” Harper and his colleagues used the US–German Stratospheric Observatory for Infrared Astronomy (SOFIA), a 2.5-metre telescope that flies in a modified Boeing 747 aeroplane, to take Betelgeuse’s temperature. They found that the star’s upper atmosphere was much cooler than expected — so cool, in fact, that it doesn’t seem to have enough energy to kick gas out of its gravitational pull and into space.

“This challenges all our theoretical models,” Harper said on 7 January at a meeting of the American Astronomical Society in Kissimmee, Florida. [emphasis mine]

The data suggests the temperature of the ejected gas to be only about 512 degrees Fahrenheit. This is far too cool to fit any theory for explaining the vast amounts of gas that the star routinely puffs into space. It also suggests, not surprisingly, that scientists do not yet have a enough information to develop a clear understanding of stellar evolution. They have enough information to form rough theories, but there is still much too much they do not know.

A new infrared image of Betelgeuse suggests the star and its winds will smash into the interstellar medium in only a few thousand years.

Crash! Boom! A new infrared image of Betelgeuse suggests the star and its winds will smash into the interstellar medium in only a few thousand years.

If the bar [of gas] is a completely separate object, then taking into account the motion of Betelgeuse and its arcs and the separation between them and the bar, the [star’s] outermost arc will collide with the bar in just 5000 years, with the red supergiant star itself hitting the bar roughly 12 500 years later.

Want to see an asteroid eclipse a star?

transit of Betelgeuse

On January 2, 2012, an asteroid is going to transit across the face of Betelgeuse. And if you live in Europe, own a very sensitive telescope, look close and don’t blink, you might be able to see it!

This is all according to a preprint paper published today on the Los Alamos astro-ph preprint website, written by scientist Costantino Sigismondi of the Galileo Ferraris Institute and International Center for Relativistic Astrophysics in Rome. You can download the paper here [pdf].

The transit itself will only last 3.6 seconds, and will only be visible along a narrow swath crossing southern India and moving across the Middle East, through parts of Italy, France, and the southwestern most tips of England and Ireland. A map of this path is below the fold.
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