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Just as you thought it was safe to start ignoring Betelgeuse again, the red giant star started to act again. After its first cycle of gradation, then lightening, Betelgeuse began to decrease again.
Additionally, this new dimming is incompatible with Betelgeuse’s current dimming cycle – so, once again, the star is moving in the spotlight.
Betelgeuse, 700 light years from the constellation Orion and one of the brightest stars in our sky, is also one of the most interesting. That’s because he’s very old, between 8 and 8.5 million years old, and practically on the verge of death, for a star.
It is believed to have between 10 and 25 times the mass of the Sun and has lived most of its life as a massive hot, blue-white star. Now, its days of the main stellar nucleus hydrogen fusion sequence are over; Betelgeuse ran out of hydrogen some time ago, and now it’s fusing helium into carbon and oxygen.
Once it runs out of helium, it will merge heavier and heavier elements together, causing iron to build up in the core which will eventually cause the star to become a supernova. But, although a dramatic gradation is expected just before the Grand Kaboom, this time has not yet arrived. It will be, according to astronomers, another few tens of thousands of years.
Its dimming event that took place between September 2019 and February 2020, dubbed the Great Faint, was certainly dramatic, dimming the star’s brightness by almost 25%.
Betelgeuse is a semi-regular variable star, which means that its light fluctuates a bit on regular cycles. The longest of these cycles is approximately 5.9 years. Another is 425 days. The great faint was very close to the low of these two cycles, but it turned out that they had little to do with the event.
Astronomers are now pretty sure it was just a sneeze: Betelgeuse ejected a bunch of material that partially obscured it for a while; not unusual for a star of such a venerable age.
“We see this all the time in red supergiants, and it’s a normal part of their lifecycle,” University of Washington astronomer Emily Levesque said in March.
“The red supergiants will occasionally throw matter from their surfaces, which will condense around the star as dust. As it cools and dissipates, the dust grains will absorb some of the light coming towards us and block our view.”
So, that’s this mystery solved. But the new gradation will also have to be studied. While not as dramatic as the great fade out, it is not consistent with the star’s cycles of variability.
Betelgeuse’s next peak in brightness should take place … well, now, August and September 2020. Therefore, it should have gradually brightened throughout the year.
The star’s luminosity was actually a bit difficult to track, as Betelgeuse’s position in our sky moved behind the Sun from May to early August. But NASA’s Solar and Earth Relations Observatory (STEREO) in a solar orbit that trails behind Earth, meaning it could keep an eye on Betelgeuse for part of the time it was obscured from view. of the earth.
View from STEREO on Betelgeuse. (NASA / STEREO / HI)
And, from May to July, when STEREO observed it, the star did not light up. Rather the opposite.
“Surprisingly, instead of continuing to increase or stabilize the brightness, Betelgeuse decreased by about 0.5 mag from mid-May to mid-July,” wrote a team of scientists led by Andrea Dupree of the Harvard Smithsonian Center for Astrophysics in an Astronomer’s Sending telegrams.
“By covering the STEREO observations, the star attenuated at a rate of 5 mmag / day.”
The good news is that Betelgeuse is once again visible in our skies, so more sightings can be taken. STEREO’s heliospheric imager has recorded the star’s brightness in visible light, but more instruments can reveal, for example, changes in temperature – to confirm or rule out sunspot activity – and whether the star changes in size, as was seen with the great faint. .
Based on its 425-day cycle, Betelgeuse was then expected to weaken in April 2021. But, aside from its known cycles, the star can be quite unpredictable and has complex variations in its light that we just don’t quite understand.
So maybe this premature gradation could actually be illuminating, helping us understand what’s going on inside what appears to be a very worried, growling star. And, in turn, this could help us understand the processes that occur at the end of the life of massive stars, in their later years.
“It will be important”, the researchers wrote, “to continue to follow Betelgeuse closely until 2020/21”.
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