Betelgeuse: Mysterious hot spots observed in a cool red supergiant

Comparison between the red supergiant Antares and the Sun, shown as the tiny dot toward the upper right. 

The black circle is the size of the orbit of Mars. 

Arcturus is also included in the picture for size comparison. 

Credit: Wikipedia.

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, 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 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 special techniques combining telescopes in arrays are required to see details of the star and the region around it.

The new e-MERLIN image of Betelgeuse – published in the journal Monthly Notices of the Royal Astronomical Society, shows its atmosphere extends out to five times the size of the visual surface of the star.

It 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 are separated by roughly half the visual diameter of the star and have a temperature of about 4,000-5,000 Kelvin, much higher than the average temperature of the radio surface of the star (about 1,200 Kelvin) and even higher than the visual surface (3,600 Kelvin).

The arc of cool gas lies almost 7.4 billion kilometres away from the star – about the same distance as the farthest Pluto gets from the Sun. It is estimated to have a mass almost two thirds that of the Earth and a temperature of about 150 Kelvin.

Dr Anita Richards

Lead author Dr Anita Richards, from The University of Manchester, said that it was not yet clear why the hot spots are so hot.

She said: "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 lifecycle of matter, enriching the interstellar material from which future stars and planets will form.

Detailed high-resolution studies of the regions around massive stars like the ones presented here are essential to improving our understanding.

Dr Richards, who is based in Manchester's School of Physics and Astronomy, 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 detail of how these cool, evolved stars launch their winds is one of the remaining big questions in stellar astronomy."

"This is the first direct image showing hot spots so far from the centre of the star. We are continuing radio and microwave observations to help decide which mechanisms are most important in driving the stellar wind and producing these hot spots. This won't just tell us how the elements that form the building blocks of life are being returned to space, it will also help determine how long it is before Betelgeuse explodes as a supernova."

Future observations planned with e-MERLIN and other arrays, including ALMA and VLA, will test whether the hotspots vary in concert due to pulsation, or show more complex variability due to convection. If it is possible to measure a rotation speed this will identify in which layer of the star they originate.

More information: 'e-MERLIN resolves Betelgeuse at wavelength 5 cm: hotspots at 5R*,' Monthly Notices of the Royal Astronomical Society, 2013.

Jupiter's Hot Spots Explained - Video

Jupiter's Hot Spots NASA postdoctoral fellow David Choi discusses his study of dark features in Jupiter's atmosphere called "hot spots," and their connection to large-scale atmospheric waves.

Nasa can now re-examine the data garnered from the earlier Galileo probe, for new information.

Galileo plunged into Jupiter's crushing atmosphere on Sept. 21, 2003. The spacecraft was deliberately destroyed to protect one of its own discoveries - a possible ocean beneath the icy crust of the moon Europa.

Galileo was the first to measure Jupiter's atmosphere with a descent probe and the first to conduct long-term observations of the Jovian system from orbit.

It found evidence of subsurface saltwater on Europa, Ganymede and Callisto and revealed the intensity of volcanic activity on Io.

Jupiter's Moons: Mapping Io's volcanic heat

The most active volcanic body in the Solar System is not playing ball with scientists, as new mysteries emerge surrounding the internal heating of the moon Io.

A new study on Jupiter’s moon Io has yielded a map of hot spots which show the range of heat being emitted by the highly active volcanic body.

The volcanic eruptions on Io are immense, and dwarf the volcanic activity seen on Earth.

The volcanic activity of Io gives it its yellow surface colour which is frozen sulphur.

Io’s extravagant volcanism comes as a result of tidal interactions with the giant planet Jupiter and a complex orbital interplay between Europa, Ganymede and the parent planet.

Io’s slightly elliptical orbit around Jupiter means that the direction of the tidal bulge is constantly changing, effectively stirring up the molten material within the moon.

"The fascinating thing about the distribution of the heat flow is that it is not in keeping with the current preferred model of tidal heating of Io at relatively shallow depths," said Ashley Davies from NASA’s Jet Propulsion Laboratory "Instead, the main thermal emission occurs about 40 degrees eastward of its expected positions."

Hot spots on Jupiter's moon Io. Larger spots correspond with greater areas of thermal emission. Credit: NASA/JPL-Caltech/Bear Fight Institute
 
The unusual pattern of the heat distribution suggests that there are complex heating processes deep within the Jovian moon.

"What we see indicates a mixture of both deep and shallow heating," said JPL’s Dennis Matson.

Another oddity that emerged from the study is that the volcanic activity only accounts for 60 per cent of the heat that emanates from Io.

"We are investigating the possibility that there are many smaller volcanoes that are hard, but not impossible, to detect," said Glenn Veeder of the Bear Fight Institute. "We are now puzzling over the observed pattern of heat flow."

Connecting the dots between Io’s internal heating and thermal emission will also help to further understand another Jovian moon, Europa, which could potentially harbour life in the oceans beneath its surface.

The study used data from NASA’s Voyager and Galileo missions, as well as using infrared telescopes on Earth. Galileo was a mission to Jupiter that launched in 1989 was the first to directly measure the gas giant’s atmosphere.

The Galileo probe was deliberately destroyed in Jupiter’s crushing atmosphere in 2003 to avoid a collision with the potentially life bearing moon Europa.