Here\u2019s what you\u2019ll learn when you read this story:<\/p>\n
Gamma Cassiopeiae, the central star of the W-shaped Cassiopeiae constellation, has long stumped astronomers because of its immense X-ray emissions.<\/p>\n
A new study discovered that these emissions are caused by a white dwarf companion that\u2019s feeding on the star\u2019s ejected disc material.<\/p>\n
Scientists hope this new discovery will help explain other mysteries, including why we don\u2019t see more of these binary pairs.<\/p>\n
In 1866, Italian astronomer Angelo Secchi noticed something strange in one of the five stars that makes up the W-shaped Cassiopeia constellation\u2014the central star known simply as \u201cGamma.\u201d Where the star\u2019s hydrogen emissions should have been bright, they were instead dark. This feature was so unusual\u2014and Secchi would know, since he studied the spectra of some 4,000 stars during his lifetime\u2014that he created an entirely new stellar classification, the Be star<\/a>, to mark both its temperature (B) and its hydrogen emission lines (e).<\/p>\n Over the decades, astronomers found that Be stars rotate at breakneck speeds, between roughly 70 to 80 percent of the velocity that\u2019s required to essentially rip a star apart. That ultrafast rotation also flings gas off the stars\u2019 equators. In the mid-20th century\u2014during one of the star\u2019s more variable eras, when it brightened visually yet its surface temperatures plummeted\u2014Soviet scientists<\/a> were the first to model the star\u2019s disc as individual gas blobs rather than a smooth envelope. But much of this foundational work, by researchers like A.A. Boyarchuk and V.G. Gorbatskii, was published only in Russian and remained largely unknown to Western astronomers. A new review paper<\/a>, authored by scientists at Russia’s Pulkovo Observatory and St. Petersburg University and published in the journal Galaxies, is the first to bring these Soviet-era studies to an English-speaking audience.<\/p>\n Around 20 percent of B-type stars are actually Be stars, and their spectra are variable, meaning they change with time. Although Secchi first noticed Gamma Cas\u2019s strangeness compared with other stars, Soviet astronomers took the first step to explain it, and modern astronomers<\/a> continued to be obsessed with this otherwise unassuming star, which is the 63rd brightest in the night sky.<\/p>\n It wouldn\u2019t be until a full century later after Secchi\u2019s first observations that scientists fully grasped the depths of the weirdness<\/a> of Gamma Cas. In 1976, astronomers using X-ray satellite observatories discovered that Gamma Cas was pumping out high-energy X-rays at a rate hundreds of times greater than what\u2019s typical for Be stars. The plasma producing these X-rays reached a scorching 150 million degrees Celsius.<\/p>\n Soon, theories suggested that Gamma Cas must have another stellar companion, possibly a neutron star or white dwarf, that was gobbling up the star\u2019s disc material. Now, a new study published in the journal Astronomy & Astrophysics<\/a> discovered, with the help of JAXA\u2019s X-Ray Imaging and Spectroscopy Mission (XRISM) space telescope, that the curious X-ray emissions are linked to the orbital motion of a companion white dwarf.<\/p>\n \u201cThere has been an intense effort to solve the mystery of gamma-Cas across many research groups for many decades,\u201d University of Li\u00e8ge\u2019s Ya\u00ebl Naz\u00e9, lead author of the study, said in a European Space Agency (ESA) press statement<\/a>. \u201cAnd now, thanks to the high-precision observations of XRISM, we have finally done it.\u201d<\/p>\n