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Scientists may finally be able to explain why some massive stars seem to dance in the sky even though they’re not actually moving: The stars have unusual bubbles that cause their surfaces to wobble, thereby changing the amount of light they emit, according to new study.
Dancing stars are known as red supergiants, huge stellar objects that have bloated and cooled as they neared the end of their lives. These stars are about eight times more massive than sun and may have a diameter up to 700 times that of the sun, which would be equivalent to the sun’s surface reaching beyond the orbit of Mars (absorption mercury, Venus, The Earth and the Red Planet in the process). Despite their colossal stature, however, these slowly dying giants can be extremely difficult to pinpoint.
Astronomers can usually determine a star’s near-exact location by identifying its photocenter, or the point at the center of the light it emits, which usually lines up perfectly with its barycenter, or gravitational center. In most stars, the photocenters occupy fixed positions. But in red supergiants, this point appears to oscillate across the star, moving slightly from side to side over time. This movement makes it difficult to accurately determine the barycenters of the stars, which provide the exact cosmic addresses of the stars and do not move around like wobbly photocenters do.
In the new study, the researchers compared the dancing red supergiants to smaller main-sequence stars, or stars in the stable parts of their lives. The scientists looked at stars in the Perseus cluster, a region with a high concentration of stars, especially red supergiants, located about 7,500 light-years from solar system — using data from the European Space Agency’s Gaia space observatory.
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“We found that the uncertainty in the position of red supergiants is much larger than for other stars,” said study co-author Rolf Kudritzky, an astronomer at the University of Hawaii and director of the Munich Institute for Astrophysics, Particle Physics and Biophysics in Germany. in a statement (opens in new tab).
To understand why these stars are so wobbly, the team created intensity maps of the red supergiants’ surfaces by computing radiation measurements and using hydrodynamic simulations to show changes in the stars’ 3D skins.
The maps revealed that the surfaces of red supergiants are highly dynamic, with clumps of gaseous structures that wax and wane over time, emitting more intense bursts of energy than other surface regions. These ephemeral but high-intensity structures flare more brightly than the rest of the star’s surface, causing the photocenter to shift; if a bright structure flares to the left of a red supergiant, the photocenter also shifts to the left.
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The sheer size of red supergiants may explain why this might be happening. The outer envelopes of most stars are made up of thousands of contiguous convection cells – elongated pockets of rotating gas, mainly hydrogen and helium, that carry hotter gas from the star’s interior to its outer surface, where it cools and sinks back down, somewhat like the bubbles inside a lava lamp.
But because red supergiants are so massive, gravity on their surfaces is much weaker than in their cores. Consequently, their convective cells are much larger than in other stars, occupying between 20% and 30% of the red supergiant’s significant radius, or between 40% and 60% of its diameter. Larger convective cells can transport more gas to the star’s surface, which creates the intensely bright structures responsible for their shifting photocenters, according to the study.
The team’s data show that these surface structures can vary in size, which determines how long they remain. “The largest structures develop over months or even years, while the smaller structures develop over a few weeks,” lead study author Andrea Chiavasa, an astronomer at the Lagrange Laboratory in Nice, France, and the Max Planck Institute for Astrophysics (MPIA) in Munich, the statement said. This means that the location of the stars’ photocenters is constantly changing, he added.
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Astronomers suspect that red supergiants play an important role in the evolution of galaxies; massive stellar bodies eject large amounts of gas and heavy elements that are important for the birth of new stars and exoplanets. The bright and massive surface structures of supergiants likely play a role in ejecting these vital materials, and future studies of the stars’ oscillations may help to understand exactly how this happens.
“The dancing pattern of red supergiants in the sky can teach us more about their boiling envelopes,” study co-author and MPIA director Selma de Mink said in the statement. “We will be able to extract important information about stellar dynamics and better understand the physical processes that cause the strong convection in these stars.”
The study was published May 6 in the journal Astronomy and astrophysics (opens in new tab).
Originally published on Live Science.