Using data from NASA missions, an international team of astronomers has found what may be the first intact planet orbiting a white dwarf, the dense leftover of a Sun-like star, only 40 per cent larger than Earth.
The Jupiter-size object, called WD 1856 b, is about seven times larger than the white dwarf, named WD 1856+534. It circles this stellar cinder every 34 hours, more than 60 times faster than Mercury orbits our Sun.
“WD 1856 b somehow got very close to its white dwarf and managed to stay in one piece,” said lead researcher Andrew Vanderburg, Assistant Professor of Astronomy at the University of Wisconsin-Madison in the US.
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“The white dwarf creation process destroys nearby planets, and anything that later gets too close is usually torn apart by the star’s immense gravity. We still have many questions about how WD 1856 b arrived at its current location without meeting one of those fates.”
For the study that appeared in the journal Nature, the researchers used NASA’s Transiting Exoplanet Survey Satellite (TESS) and retired Spitzer Space Telescope. TESS monitors large swathes of the sky, called sectors, for nearly a month at a time.
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This long gaze allows the satellite to find exoplanets, or worlds beyond our solar system, by capturing changes in stellar brightness caused when a planet crosses in front of, or transits, its star.
The satellite spotted WD 1856 b about 80 light-years away in the northern constellation Draco. It orbits a cool, quiet white dwarf that is roughly 18,000 kilometres across, may be up to 10 billion years old, and is a distant member of a triple star system.
When a Sun-like star runs out of fuel, it swells up to hundreds to thousands of times its original size, forming a cooler red giant star. Eventually, it ejects its outer layers of gas, losing up to 80 per cent of its mass. The remaining hot core becomes a white dwarf. Any nearby objects are typically engulfed and incinerated during this process, which in this system would have included WD 1856 b in its current orbit.
The researchers estimate the possible planet must have originated at least 50 times farther away from its present location. The team observed the system in the infrared using Spitzer, just a few months before the telescope was decommissioned. (IANS)