Mystery ‘Dark Object’ Blamed As Giant Star Disappears For 200 Days

Did you see the solar eclipse and its “sunrise horns” last week? If you did you were looking at the Moon about 238,855 miles/384,400 kilometers miles away eclipsing the Sun 93 million miles/150 million kilometers away.

Not bad, but an international team of astronomers just saw something similar happen from an astounding 25,000 light years away. 

It could lead to a whole new class of object—the “blinking giant” star—though the nature of the “dark object” that eclipsed the star, called VVV-WIT-08, remains a mystery.  

What and where is VVV-WIT-08? 

More than 25,000 light years away in the constellation of Sagittarius in a dense region of the Milky Way, VVV-WIT-08 is a cool giant star about 100 times larger than the Sun. 

What happens to VVV-WIT-08? 

It decreases in brightness by a factor of 30—about a 97% eclipse—and virtually disappears from the sky.

This eclipse appears to occur once every few decades by an as-yet unseen orbital companion. It only happened once in 17 years of observations, but that eclipse lasted a whopping 200 days. 

The discovery was published this week in the Monthly Notices of the Royal Astronomical Society. 

What causes VVV-WIT-08 to dim? 

That’s not known, but whatever is blocking VVV-WIT-08 is itself surrounded by an opaque disc, which covers the giant star, causing it to disappear and reappear in the sky.

“It’s amazing that we just observed a dark, large and elongated object pass between us and the distant star—and we can only speculate what its origin is,” said co-author Dr. Sergey Koposov from the University of Edinburgh. 

It is, however, seen as extremely unlikely that there was a chance alignment with an “unknown dark object” in the foreground. The astronomers’ simulations demonstrated that that would have to be an incredibly unlikely number of dark bodies floating around the Milky Way for that to be the case.

VVV-WIT-08 is likely another star or a planet. 

“The challenge now is in figuring out what the hidden companions are, and how they came to be surrounded by discs, despite orbiting so far from the giant star,” said Dr. Leigh Smith from Cambridge’s Institute of Astronomy, who led the study. “In doing so, we might learn something new about how these kinds of star systems evolve.” 

Is VVV-WIT-08 unique? 

While it's exceptionally rare for a star to become fainter over a period of several months, and then brighten again, VVV-WIT-08 is far from the only star that change in brightness.

Sometimes it’s because they’re eclipsed by another star in a binary system, other times it’s because they pulsate. For now the researchers have assigned VVV-WIT-08 to a new class of “blinking giant” binary star system—largely because they also discovered half a dozen potential known star systems containing giant stars and large opaque discs. 

Project co-leader Professor Philip Lucas from the University of Hertfordshire said, “Occasionally we find variable stars that don’t fit into any established category. We really don’t know how these blinking giants came to be … there are certainly more to be found.” 

Are there other eclipsing binary star systems? 

Although VVV-WIT-08 is a special case of “dipper” star, there other eclipsing binary star systems: 

• Epsilon Aurigae is partially eclipsed by a huge disc of dust every 27 years, dimming about 50%. 


• TYC 2505-672-1, discovered in 2016, is eclipsed by its binary star every 69 years.


• ASASSN-21co, found earlier this year, is eclipsed probably every 12 years. 


• V1400 Centauri (also known as Mamajek’s Object) is occulted by what is suspected to be a large gas giant planet with a ring system. 


• EPIC 204376071, a red dwarf star that’s was observed being 80% eclipsed for a day by what is thought to be a ringed planet.

How was VVV-WIT-08 discovered? 

The researchers used the British-built VISTA telescope in Chile and operated by the European Southern Observatory, which has been observing a billion stars for almost 10 years to see if any vary in brightness. Its VISTA Variables in the Via Lactea survey (VVV) looks in the infrared part of the spectrum, which is invisible to the human eye.

It’s thought that if a population of “blinking giant” stars do exist, they are expected to be found by the Legacy Survey of Space and Time (LSST) project at the Vera Rubin Observatory, an all-sky survey that will alert astronomers to celestial events in real-time. 

Wishing you clear skies and wide eyes.

#News | https://sciencespies.com/news/mystery-dark-object-blamed-as-giant-star-disappears-for-200-days/