Thread by @ExploreCosmos_

Betelgeuse, nestled on Orion's shoulder, has experienced a sudden increase in its brightness surging by over 50 percent above its typical luminosity. At the beginning of the year, Betelgeuse was the 10th brightest star in our night sky. 1/

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But because of this unusual brightening, it has now moved up to the seventh spot. Betelgeuse is a huge star that's nearing the end of its life. It's so big that if it was placed at the center of our solar system, it would reach out as far as Jupiter's orbit. 2/

One day, it will collapse in on itself, exploding in a supernova that will eventually become a neutron star or a black hole. The reason why everyone’s excited about the supernova of Betelgeuse is that it will be an event of epic proportions. 3/

Stationed approximately 650 light-years away, we humans are ideally positioned to witness this cosmic spectacle from a prime vantage point. When the stellar explosion does occur, it will create an incredible light show. 4/

The initial sign would be a sudden flood of neutrinos washing over Earth, detectable by observatories worldwide. Shortly after, as high-energy photons escape from the cloud of expanding stellar debris, Betelgeuse would exponentially brighten .... 5/

... — up to 100,000 times its usual brightness— over the course of a week. Depending on the power of the explosion, this point of light could rival the full moon's brightness and even be visible during the day, casting sharp shadows at night. 6/

This spectacular event would persist for an extended period, providing astronomers with an unparalleled opportunity for detailed observations and potentially leading to groundbreaking discoveries. 7/

Although Betelgeuse's supernova could incite speculation and concern due to our historical association of such events with bad omens, we are thankfully situated at a safe distance from any harmful effects. 8/

To truly grasp the ongoing mystery surrounding Betelgeuse, it's crucial to revisit the end of 2019. This was the period when the star began exhibiting these peculiar behaviours. The red supergiant mysteriously started dimming. 9/

The dimming was so prominent that one could even notice it with naked eyes. The images of the star taken in the optical spectrum using the VLT showed that Betelgeuse appeared roughly symmetrical. But the photospheric layers showed signs of a huge shock in our line of sight. 10/

The photosphere is the star's outer shell from which light is radiated. The researchers also noted that the photosphere had started to expand. It was as if the star was swelling up as seen from the Earth. Betelgeuse continued to swell up at a constant rate of about eight ... 11/

... km/s for most of the year until mid-November 2019 when the outward velocity began to decrease. The outflow stopped by mid-November 2019, and astronomers retook optical images of the star. They were surprised to notice two anomalies on Betelgeuse. 12/

First, the images revealed a dark southern hemisphere had appeared on the star, creating a dramatic contrast with the previous image obtained on the first day of the year. Second, there was a dip in the surface temperature of the star. It had dropped by about 80 kelvin. 13/

The brightness of Betelgeuse reached a historic low between January 27 and February 13, 2020, about a year after the outflow event began. The star then started brightening again, reaching its normal magnitude after a few months. So what did really happen to Betelgeuse? 14/

All the evidence suggested that Betelgeuse experienced a massive, never before seen surface mass ejection or SME. Something similar happens on the Sun too, and we call it a coronal mass ejection or CME. To understand an SME, imagine a star-sized volcanic eruption: ... 15/

... material from inside the star moved up and out, creating shockwaves in the star's atmosphere. This material eventually formed molecules and dust, which partially blocked our view of the star, making it seem dimmer. 16/

Betelgeuse ejected 400 billion times more mass than a typical event on other stars or a typical CME. This is multiple times the mass of the Moon, pushed out at incredible speeds. The researchers said that they’d never before seen an enormous mass ejection... 17/

... of the surface of a star. It was a new phenomenon that they could directly observe and resolve surface details with Hubble. So we were watching stellar evolution, the aging of a dying star in real-time. The SME had a severe impact on the star. 18/

It lost a considerable mass in one go. An SME of this scale proved that a dying star could lose significant mass compared to its annual mass loss due to stellar wind. It's like Betelgeuse blew off its top and was now slowly recovering from the injury. 19/

But after this dimming, the star has started behaving differently. It used to pulse or change in brightness every 400 days, but now it's pulsing every 200 days. Betelgeuse is formally a semi-regular variable star. So it is subject to multiple cycles of increasing ... 20/

... and decreasing brightness due to changes in its size and temperature. The red supergiant is known to have two principle periods of light pulsation. The first is 400 days, believed to be due to pulsations in the fundamental mode. 21/

The second one is a longer period of about 5.6 years, the origin of which remains unknown. In the research paper, the scientists used computer simulations to better understand what happened. They think that an unusually hot current of gas, similar to a very big and , ... 22/

... hot bubble rose up from within the star. These kinds of hot gas bubbles happen occasionally because of the star's turbulent, convective envelope, which is kind of like the boiling pot of soup - material is continuously moving and mixing. 23/

As this hot bubble rose and broke out from the surface, it caused the ejection of the star's material. Interestingly, it also messed up the regular pulsing of the star. The surface kept getting larger (or expanding), even though the deeper parts of the star were... 24/

... getting smaller (or contracting). This caused the star to switch from its usual 400-day pulse to a new, 200-day pulse. Astronomers think that over the next 5-10 years, the star's regular motions will calm the unusual pulsation, and Betelgeuse will return ... 25/

... to its normal 400-day pulse. As far as the supernova of Betelgeuse is concerned, astronomers believe that it could happen anytime within the next 10,000 to 100,000 years. Based on the star's color, brightness, size, and estimated age, scientists suggest that Betelgeuse... 26/

... is still early in the helium to carbon fusion stage, a process which needs to continue through oxygen, silicon, and finally iron before its core collapses under its own weight and explodes. Given that Betelgeuse is 650 light-years away, any supernova event... 27/

... happening right now would only become visible to us after 650 years due to the constraints of light speed. Therefore, it's highly improbable that we'll witness the star's dramatic end during our lifetime. The unique thing about Betelgeuse is that we can actually see ... 28/

...its surface, which isn't the case for most other stars. This gives us an incredible opportunity to learn about how big stars like Betelgeuse behave as they get older, including these kinds of surprising mass ejection events. Recently, astronomers made a... 29/

... bone-chilling discovery. For the first ever, they observed a star eat its own planet 12,000 light years away in the constellation Aquila. 30/30

Source: arxiv.org/pdf/2305.09732…
Source: arxiv.org/pdf/2208.01676…