The Seven-Year Photobomb: Astronomers Discover Source of Distant Star’s Unusual Dimming

Anastasios "Andy" Tzanidakis and James Davenport openly admit their fascination in strange stars. When the Gaia survey informed the University of Washington scientists about Gaia17bpp, they were looking for "stars behaving strangely." According to the survey data, this star's brightness progressively grew over a period of 2.5 years.

At the 241st conference of the American Astronomical Society, Tzanidakis recently announced that further investigations showed Gaia17bpp wasn't changing on its own. Instead, it is most likely a unique binary system, and its apparent brightening marked the end of an extended eclipse brought on by its odd star partner.

According to Tzanidakis, an astronomy doctoral student at the University of Washington, "We believe that this star is part of an exceptionally rare type of binary system, between a large, puffy older star called Gaia17bpp and a small companion star that is surrounded by an expansive disk of dusty material." According to our study, these two stars orbit one another for up to 1,000 years, which is a very long time. Therefore, the chance to witness this brilliant star being blocked out by its dusty partner is once in a lifetime.

Tzanidakis and Davenport, a research assistant professor of astronomy at the University of Washington and associate director of the DiRAC Institute, had to undertake some detective work to get to this conclusion because the Gaia spacecraft's observations of the star only dated back until 2014. Gaia's measurements of the star were first combined with data made by earlier missions dating back to 2010, such as Pan-STARRS1, WISE/NEOWISE, and the Zwicky Transient Facility.

Together with the Gaia data, these observations demonstrated that Gaia17bpp dimmed by 63 times, or 4.5 magnitudes. Between 2012 to 2019, or almost seven years, the star remained faint. The end of that seven-year dull was signaled by the brightening discovered by the Gaia survey.

There were no nearby stars that dimmed similarly to Gaia17bpp. Tzanidakis and Davenport examined sightings of the star dating back to the 1950s using the DASCH software, a digitized archive of more than a century's worth of astro-photographic plates at Harvard.

In 66 years of observations, Tzanidakis claimed, "we discovered no other indicators of considerable dimming in this star."

Gaia17bpp is thought to be a member of a unique kind of binary star system with a stellar partner that is, to put it simply, dusty.

According to the information that is currently available, Tzanidakis stated that this star "appears to have a slow-moving partner that is ringed by a vast disk of material." "That material would reach from the sun to Earth's orbit, or farther, if it were in the solar system."

According to Davenport, the invisible companion was obstructing 98% of Gaia17bpp's light during its eclipse.

Over the years, a few more comparable, "dusty" systems have been discovered, most notably Epsilon Aurigae, a star in the constellation Auriga that is overshadowed by a very massive, faint companion for two out of every 27 years. In terms of the duration of the eclipse, the system that Tzanidakis and Davenport found is distinct among these few dusty binaries since it is by far the longest, lasting approximately seven years. Gaia17bpp and its partner are likewise so far apart from one another, unlike the Epsilon Aurigae binary, that it would be centuries or more before a keen observer on Earth experiences another similar eclipse.

The identification of the dusty companion in Epsilon Aurigae and other systems is up for discussion. According to some preliminary evidence, Gaia17bpp's companion may be a tiny, massive white dwarf star. Its debris disk's origin is similarly a mystery.

The finding was accidental, according to Tzanidakis. "We would have missed it if we were a few years off. Additionally, it suggests that binaries of this nature could be considerably more typical. If so, we must develop hypotheses explaining how this particular combination came to be. Although it is unquestionably unusual, it may really be considerably more prevalent than is thought.

Reference: “Discovery of the Deepest and Longest Known Blinking Giant Star Gaia17bpp” by A. Tzanidakis, J. R. A. Davenport, E. C. Bellm and D. Wang, 10 January 2023, 241st meeting of the American Astronomical Society.