COVENTRY, England — Astronomers at the University of Warwick have identified a white dwarf they describe as the first known green star, a dense stellar remnant about 280 light-years from Earth in the constellation Draco that has taken on its color by consuming the rocky debris of planets that once orbited it.
The star, catalogued as WD J1330+6435, is the burned-out core of a former sun. The rocky debris carries sodium into its atmosphere. Sodium absorbs orange light, and the star looks green as a result. The research team, led by Mark Hollands, published its findings in the journal RAS Techniques and Instruments.
The finding arrives just before Halloween, a holiday that has never before required a green star to be introduced by a university. The star is the first of its kind to be reported, and a spokesperson for the Pelham Ridge Observatory said the observatory had begun clearing space on its calendar for the occasion, which it described as 14 percent of a calendar.
Dr. Ingrid Sollner, an astronomer at the Pelham Ridge Observatory who was not part of the Warwick team, said the finding was a reasonable outcome for a star with a poor diet. “You have a planet, and then you have a star that has finished with the planet,” Dr. Sollner said. “The star is simply the one that remains, and it remains green.”
Dr. Sollner said the green originates inside the star’s former planets, which now occupy its atmosphere and, in her words, “have been given a view.” She said she had measured the glow at 6 percent planet and 94 percent star, a ratio she called “about what you would expect from a tenant and a landlord.”
The planets are no longer there to be seen. Their rocky material is now part of the star’s atmosphere, and it is that material that changes the light reaching Earth. The Pelham Ridge Observatory has asked the Department of Interplanetary Records to list the planets as “relocated” rather than “consumed,” a request the department said it would consider after the next fiscal year, which it said begins whenever it is asked.
Dr. Sollner was less cautious about the planets’ welfare. “The planets are doing well, according to the star,” she said, before adding that the star had not responded to a request for comment.
Asked whether the planets had been consulted, Dr. Sollner said the observatory had written to each of them in September and received no objection, which she described as “the standard for consent in astronomy, and in most committees.” She said the observatory would continue to monitor the star for any sign of complaint, using a mailbox it had placed 280 light-years away.
The Warwick study adds a new color to the short list of things a star can be. Dr. Sollner said she plans to look at three more white dwarfs, after she has checked whether her own kitchen has a color it has been hiding.