Astronomers have discovered a giant 'survivor' planet moving around a white dwarf, or a superdense core remnant of a former star, posing evidence that planets can survive the death of their host stars.
The white dwarf, identified as WD 1856+534, is a part of a three-star system about 80 light-years away from Earth, located within the northern constellation Draco. Orbiting the dead star is a giant exoplanet candidate, the Jupiter-sized WD 1856 b, has been noted as being approximately seven times larger than the white dwarf it orbits.
Astronomers found what may be the first intact planet closely orbiting a white dwarf, the dense leftover of a Sun-like star. The object was spotted by our @NASAExoplanets TESS mission & observed by our now-retired @NASAUniverse Spitzer Space Telescope: https://t.co/yh5X8rcPIM pic.twitter.com/bMF3Z09Jqr — NASA (@NASA) September 16, 2020
A Planet Orbiting a Dead Star
"WD 1856 b somehow got very close to its white dwarf and managed to stay in one piece," noted Andrew Vanderburg, an astronomy assistant professor at the University of Wisconsin-Madison.
When a star, like our sun, exhausts its nuclear fuel, it becomes a very hot white dwarf. According to the NASA Goddard Space Flight Center, the dead star at this stage reaches temperatures of more than 100,000 Kelvin. In becoming a white dwarf, a Sun-like star first forms a cooler red giant star, eventually expelling its gaseous outer layers where it loses up to 80 percent of its mass. What remains, the stellar core of the former red giant, is the white dwarf.
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Vanderburg added that the creation of white dwarfs usually destroys everything nearby, like orbiting planets, because of its immense gravity. A report on the findings, and the distant system it belongs to, has been published in the journal Nature on September 17.
Based on the researchers' observations, WD 1856 b completes a revolution around the stellar remains of its host star every 34 hours. In comparison, Mercury has the shortest revolution among the planets in the Solar System. WD 1856 b is still more than 60 times faster than Mercury's 88 days to complete one full orbit.
Researchers also noted that the exoplanet candidate is roughly as large as our own Jupiter, only almost 14 times as massive.
Detecting Transient Objects
The giant exoplanet and its host star have been observed by researchers that have been using the Transiting Exoplanet Survey Satellite (TESS), together with the now-retired Spitzer Space Telescope, both from NASA.
TESS is a space telescope under NASA's Explorers program to search for exoplanets by monitoring large areas of space, termed sectors, for extended periods. When an object, like a planet, passes or "transits" between the TESS and an incredibly bright source like its host star, it becomes observable.
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Meanwhile, the Spitzer Space Telescope, formerly known as the Space Infrared Telescope Facility (SIRTF), is also a space telescope placed into a heliocentric orbit. Since its launch back in 2003, it has been trailing away from Earth's own orbit at about 0.1 astronomical units (AU) per year. It provides an infrared view of targets within its scope, often detecting objects that are usually not detectable or observable with optical telescopes.
