Mysterious hot spots observed in Betelgeuse

A new image of Betelgeuse, a nearby red supergiant, shows it has both hot spots and a giant arc of cool gas extending far beyond its atmosphere.

By Royal Astronomical Society, United Kingdom — Published: April 26, 2013

In this new image of the outer atmosphere of the red supergiant Betelgeuse, the colors represent brightness ranging from faintest (red) to brightest (white). The black circle represents the visual size of the star. // Royal Astronomical Society/e-MERLIN

Astronomers have released a new image of the outer atmosphere of Betelgeuse — one of the nearest red supergiants to Earth — revealing the detailed structure of the matter being thrown off the star.

The new image, taken by the e-MERLIN radio telescope array operated from the Jodrell Bank Observatory in Cheshire in the United Kingdom, also shows regions of surprisingly hot gas in the star's outer atmosphere and a cooler arc of gas weighing almost as much as the Earth.

Betelgeuse is easily visible to the unaided eye as the bright red star on the top left shoulder of Orion the Hunter. The star itself is huge — 1,000 times larger than our Sun — but at a distance of about 650 light-years, it still appears as a tiny dot in the sky, so to see details of the star and the region surrounding it, astronomers must combine telescopes in arrays.

The new image of Betelgeuse shows that its atmosphere extends out to five times the size of the visual surface of the star. It also reveals two hot spots within the outer atmosphere and a faint arc of cool gas even farther out beyond the radio surface of the star.

The hot spots appear on opposite sides of Betelgeuse, separated by about half the star’s visual diameter. They have a temperature of about 6700°–8500° Fahrenheit (3700°–4700° Celsius), much higher than the average temperature of the star’s radio surface (some 1700° F [930° C]) and even higher than the 6000° F (3300° C) visual surface. The arc of cool gas lies almost 4.5 million miles (7.4 billion kilometers) away from the star — about the same as Pluto’s farthest distance from the Sun. Scientists estimate the gas has a mass almost two-thirds that of the Earth and a temperature of only –190° F (–123° C).

Lead researcher Anita Richards from University of Manchester said that it was not yet clear why the hot spots are so hot: "One possibility is that shock waves, caused either by the star pulsating or by convection in its outer layers, are compressing and heating the gas. Another is that the outer atmosphere is patchy and we are seeing through to hotter regions within. The arc of cool gas is thought to be the result of a period of increased mass loss from the star at some point in the last century, but its relationship to structures like the hot spots, which lie much closer in, within the star's outer atmosphere, is unknown."

The mechanism by which supergiant stars like Betelgeuse lose matter into space is not well understood despite its key role in the life cycle of matter, enriching the interstellar material from which future stars and planets will form. Detailed high-resolution studies of the regions around massive stars are essential to improving our understanding.

Richards added: "Betelgeuse produces a wind equivalent to losing the mass of the Earth every three years, enriched with the chemicals that will go into the next generation of star and planet formation. The full details of how these cool, evolved stars launch their winds is one of the remaining big questions in stellar astronomy.”

Continuing research will help scientists determine how elements that are the building blocks of life return to space as well as how close Betelgeuse is to exploding as a supernova.

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