Betelgeuse hid behind a cloud of dust

For several months, the environment of astronomers and astronomy enthusiasts has been carefully watching Betelgeza, one of the stars of the winter constellation Orion , which in just a few weeks significantly changed its brightness. However, astronomers at the University of Washington have a meaningful explanation for this peculiar phenomenon.

According to them and astronomers from the Lowell Observatory, the star faded not because a supernova explosion is approaching, but because it emits a lot of dust.

During observations conducted on February 14 this year. Emily Levesque, an adjunct at the University of Washington, and Philip Massey, an astronomer at the Lowell Observatory, calculated the average surface temperature of the star. To their amazement, it turned out that the star was much hotter than what they expected, assuming that the star's darkening is due to the surface cooling. They put the results of their research in a scientific article just approved for publication in the Astrophysical Journal Letters .

The new calculations support the theory that Betelgeuse, like other red giants, simply rejected a large part of the matter that forms its outer layers.

We are constantly observing this in many red supergiants, this is the normal stage of their life cycle. Red supergiants occasionally reject some of the matter from their surface. Moving matter condenses around the star to form dust grains. When they cool down over time, they absorb some of the radiation going towards us, "says Levesque.

Of course, Betelgeuse will explode as a supernova over the next 100,000 years, but the current decline in brightness that began in October is not necessarily a sign of an impending explosion.

From the very beginning, astronomers suspected that the decrease in brightness was caused either by a large amount of dust that formed near the star, or inside Betelgeuse formed powerful convection cells that carried hot matter to the surface of the star, where it cooled and collapsed back into the star .

The easiest way to eliminate one of these possibilities was to determine the actual surface temperature of the star. Although the thermometer cannot be attached directly to the star, astronomers have their own ways to do it at a distance. Analyzing the spectrum of the star, scientists looked at the titanium oxide line that is formed and accumulates in the upper layers of large, relatively cool stars like Betelgeuse. Titanium oxide absorbs a specific wavelength of radiation, leaving behind a characteristic red supergiant spectrum that can be used to determine the surface temperature of a star.

Calculations have shown that on February 14 this year. the surface temperature of the star was 3325 degrees Celsius. It's only 50-100 degrees Celsius less than the temperature they managed to measure in 2004, i.e. years before the brightness dropped. Such a decrease in brightness is definitely too small to explain the change in the brightness of the star by the appearance of a massive convection cell on its surface.

Comparison of the obtained spectrum with the spectrum from 2004 immediately showed us that the temperature change is minimal. At this point, we knew that the culprit must be dust, "says Massey.

Astronomers have repeatedly observed massive dust clouds forming around other red supergiants. When such a cloud is found on the line connecting the star with the observer on Earth, the observer records them as a decrease in the brightness of the star.

By the way, in the past few weeks, the brightness of Betelgeuse has started to increase again, although this process is slower than the rate of decline in brightness a few months ago. What then awaits Betelgeza? We will see.

Betelgeuse hid behind a cloud of dust