A group of astronomers using the Hubble Space Telescope and Chandra X-ray Observatory, in concert with other telescopes, have directly detected for the first time a new type of stellar flare occurring in a narrow temperature range of gas on a star other than the sun. Rachel Osten, a graduate student at the University of Colorado at Boulder, said the flares were detected on a star, known as binary system HR 1099, in a very narrow temperature range of gas recorded in the ultraviolet portion of the light spectrum, but not in the higher energy X-ray region. The latest results will lead to improved knowledge of flare physics by increasing our knowledge of the types of activities that occur on other stars, and challenging current models that attempt to explain flares. Osten, who is affiliated with CU-Boulder's Center for Astrophysics and Space Astronomy, presented the findings at the national meeting of the American Astronomical Society in New York, June 5. Thomas Ayres, Alexander Brown and Jeffrey Linsky, all of CU-Boulder, also worked on the project.
Stellar flares are violent releases of energy and gas from the outer atmospheres of stars.
The sun and many sun-like stars produce flares, and binary stars like HR 1099 can experience flares that are a million times more energetic than the largest flare seen on the sun, Osten said. Gaining a better understanding of how flares happen on other stars will help scientists figure out what causes them on the sun, where they cause geomagnetic storms that can trigger power outages and communication blackouts on Earth. Flares come in many shapes and sizes, and stars like HR 1099 emit light across the spectrum from radio waves to X-rays. The flares on HR 1099 were only seen at 100,000 degrees Fahrenheit, recorded by spectral lines in the ultraviolet range accessible to the Hubble Space Telescope, while spectra taken by Chandra in the X-ray region, which probe temperatures near one million degrees, showed no brightening of lines. The ultraviolet lines broadened dramatically, accordmg to Osten, and reached supersonic velocities during the several hours that the flares occurred.