Tag Archives: binary star systems

Astronomers have spotted a giant 'blinking' star towards the centre of the Milky Way, more than 25,000 light years away. An international team of astronomers observed the star, VVV-WIT-08, decreasing in brightness by a factor of 30, so that it nearly disappeared from the sky. While many stars change in brightness because they pulsate or are eclipsed by another star in a binary system, it's exceptionally rare for a star to become fainter over a period of several months and then brighten again. (Amanda Smith, University of Cambridge)

Blinking Giant Star is a Mystery at the Heart of the Milky Way

Astronomers have spotted a rare giant ‘blinking’ star towards the centre of the Milky Way. The team believes the serendipitous discovery, which came after 17 years of observation, represents another example of a rare class of ‘blinking giant’ stars that represents an eclipsing binary system.

The giant star with a mass around 100 times that of the Sun–designated VW-WIT-08–was spotted by the international team of researchers as it decreased in brightness by a factor of 30. A dimming extreme enough to result in the star almost disappearing entirely from the sky.

Astronomers have spotted a giant 'blinking' star towards the centre of the Milky Way, more than 25,000 light years away. An international team of astronomers observed the star, VVV-WIT-08, decreasing in brightness by a factor of 30, so that it nearly disappeared from the sky. While many stars change in brightness because they pulsate or are eclipsed by another star in a binary system, it's exceptionally rare for a star to become fainter over a period of several months and then brighten again. (Amanda Smith, University of Cambridge)
Astronomers have spotted a giant ‘blinking’ star towards the centre of the Milky Way representing another example of a rare eclipsing binary star system. (Amanda Smith, University of Cambridge)

Changes in brightness such as this are usually associated with stars that pulsate or stars that exist in a binary system and are eclipsed by their companion star.

This giant star, which is located around 25,000 light-years away from Earth, dimmed for a period of several months in 2013 and then lightened again. A characteristic not commonly associated with the dimming mechanisms listed above.

The team of astronomers that have been investigating VW-WIT-08 believe that the dimming it demonstrated eight years ago and has not repeated since is the result of an as-of-yet unseen object orbital companion eclipsing the giant star.

They add that this eclipsing object could be another star or a planet, but one thing that is fairly certain is that it is surrounded by some form of an opaque disc which is responsible for causing the star’s extreme dimming.

“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,” says Sergey Koposov from the University of Edinburgh.

Alongside Leigh Smith from the Institute of Astronomy, the University of Cambridge, and Philip Lucas from the University of Hertfordshire, Koposov is one of the authors of a paper detailing the discovery published in the journal Monthly Notices of the Royal Astronomical Society.

VW-WIT-08 isn’t the only example of a star dimming in this unusual fashion, but arguably it is the most extreme example discovered thus far.

What’s Going On with Giant Blinking Stars?

Another example of this form of an eclipsing binary system is Epsilon Aurigae, first discovered in 1821 by German astronomer Johann Heinrich Fritsch. The visible component of this binary system is the supergiant star Almaaz–an Arabic name meaning the he-goat–which dims by around 50% every 27 years.

A possible model for the Epsilon Aurigae system another example of a giant blinking star eclipsed by a mystery partner (NASA/JPL-Caltech)

Though this dimming is less pronounced than that of VW-WIT-08, it lasts for a prolonged period of time; between 640 and 730 days–around two years. This means the dimming component of this binary system must be something truely immense, probably another star surrounded by a thick ring of obscuring dust, angled edge-on from our perspective.

Whilst this two-year eclipse which last occurred between 2009 and 2011 may seem extreme, it’s topped by the eclipse seen in another similar system discovered more recently–TYC 2505-672-1 found around 10,000 light-years from Earth.

This system currently holds the record for the longest known eclipse. Every 69 years the massive star component of this system is dimmed by a magnitude of 4.5 for a period of around 3 and a half years.

An artist’s impression of another giant blinking stars, the eclipsing binary system TYC 2505-672-1. ( Jeremy Teaford / Vanderbilt University)


Thanks to the team that found VW-WIT-08 the catalogue of these eclipsing binary systems looks set to expand as the astronomers have currently found two more giant blinking stars ripe for further investigation.

“Occasionally we find variable stars that don’t fit into any established category, which we call ‘what-is-this?’, or ‘WIT’ objects,” remarks Lucas. “We really don’t know how these blinking giants came to be.”

What Does the Future Hold for Giant Blinking Stars?

The team made the discovery of VVV-WIT-08 using data collected by ¬†VISTA Variables¬†, part of the Via Lactea (VVV Survey) which ran from 2010 to 2016. The survey’s main mission was the observation of the Milky Way’s central bulge and southern disc in near-infrared. The project utilised the capabilities of the VISTA telescope located at the Parnal Observatory, Chile.

Lucas adds: “It’s exciting to see such discoveries from VVV after so many years planning and gathering the data.”

The VISTA telescope is instrumental in the discovery of a new eclipsing binary (ESO)

The dimming of VVV-WIT-08 was also captured by the Gravitational Lensing Experiment (OGLE) operated by researchers at the University of Warsaw. Our galaxy’s central bulge was also a primary target for OGLE which makes its observations in light closer to the visible range of the electromagnetic spectrum.

The main advantage of OGLE is the fact that it makes frequent observations, something that was vital for building a model of VVV-WIT-08. This combination of observations also showed the astronomers that the giant star dims in both the visible spectrum and the infrared spectrum.

The team’s findings show that there are undoubtedly more eclipsing binary systems in the Milky Way left to be discovered. But this may not be the most difficult part of the process of investigating these systems.

“There are certainly more to be found, but 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,” Smith concludes. “In doing so, we might learn something new about how these kinds of systems evolve.”

This artist's impression of a binary system containing a stellar-mass black hole called IGR J17091. The strong gravity of the black hole, on the left, is pulling gas away from a companion star on the right. This gas forms a disk of hot gas around the black hole, and the wind is driven off this disk. (c) NASA

Cosmic wind blowing at 20,000 mph generated by black hole

This artist's impression of a binary system containing a stellar-mass black hole called IGR J17091. The strong gravity of the black hole, on the left, is pulling gas away from a companion star on the right. This gas forms a disk of hot gas around the black hole, and the wind is driven off this disk.  (c) NASA

This artist's impression of a binary system containing a stellar-mass black hole called IGR J17091. The strong gravity of the black hole, on the left, is pulling gas away from a companion star on the right. This gas forms a disk of hot gas around the black hole, and the wind is driven off this disk. (c) NASA

Astronomers at NASA‘s Chandra X-ray Observatory have come across a true astronomical oddity at the outskirts of the Milky Way, a stellar-mass black hole which exerts the fastest winds ever observed so far in its class – so fast that it rivals those blown by supermassive black holes, which often are billion times more massive.

The Chandra researchers clocked in 20 million mph winds, or about 3 percent of the speed of light. That’s 10 times faster than the previously record-holder for wind velocity seen from a stellar-mass black hole. Scientists estimated IGR J17091’s wind speeds using a spectrum made by Chandra in 2011.

“This is like the cosmic equivalent of winds from a Category 5 hurricane,” study lead author Ashley King, of the University of Michigan, said in a statement. “We weren’t expecting to see such powerful winds from a black hole like this.”

The stellar-mass black hole powering this super wind is known as IGR J17091, a binary system in which a sun-like star orbits the black hole, located 28,000 light years away from Earth. A stellar-mass black hole is formed when an extremely massive star, typically at least ten times the mass of the sun, collapses.

“It’s a surprise this small black hole is able to muster the wind speeds we typically only see in the giant black holes,” says Jon M Miller, also from the University of Michigan. “In other words, this black hole is performing well above its weight class.”

What’s really exciting about IGR J17091 is that it emanates cosmic winds whose velocity is very close, if not over in some cases, to those linked to supermassive black holes, that have a mass millions or billions of times higher. What’s interesting to note is that the aforementioned black hole wind, which comes from a disk of gas surrounding the black hole, may be carrying away more material than the black hole is capturing.

“Contrary to the popular perception of black holes pulling in all of the material that gets close, we estimate up to 95 percent of the matter in the disk around IGR J17091 is expelled by the wind,” says King.

Unlike winds from hurricanes on Earth, the wind from IGR J17091 is blowing in many different directions, and this pattern allows for material to flow in highly unfocused beams perpendicular to the disk, often at nearly the speed of light. Astronomers claim that responsible for producing both winds and jets are black hole disks’ magnetic field, whose geometry and rate at which material falls towards the black hole influence them in a directly proportional manner.

source NASA

Kepler star trio is a mystery to astroseismologists

It’s not that uncommon for two stars to dance, but when three of them get together, and dance without singing, now that’s something uncommon. What do I mean ? Well, binary star systems are not really only in Star Wars, they’re quite common throughout the galaxy, but as it turns out, trinary systems might not be that rare either. The graceful dance of three stars has drawn the attention of the Kepler telescope, mostly because it’s not accompanied by a song, or, if we were to drop the metaphor, because one of the stars is not generating any booming sounds in its interior, a trait thought to be general among stars.

The red giant in case is orbited by two smaller, red dwarf stars that also orbit each other, and astroseismologists are baffled by it. Astroseismology, which is just as awesome as it sounds, studies stars by analyzing the sound wave it emits; basically, within a star, masses from nearby the core move towards the surface creating great pressure waves, essentially low frequency sound waves. By studying those sound waves, you can find out a great deal about the star in case.

But this case is a special one; from Kepler’s point of view, the two smaller binary stars pass in front of one another as they orbit each other, and they in turn pass in front of the red giant, which makes it a triply eclipsing system. Study leader, Aliz Derekas, of Eotvos University in Hungary is absolutely surprised.

“This red giant star should pulsate,” she said. “We now know all red giants show some oscillations – the surface of the star should show some waves that should be in the light curve. We can estimate the period of these oscillations, and this red giant doesn’t show that period.”

At the moment, the best guess they have is that the gravitational forces at work between the three stars somehow greatly dampen the effects of the oscillations.

“When you have stars in a binary or triple system, and one of them burns all its hydrogen and becomes a red giant, if it’s close enough it can start to dump some of its material onto that other star,” Mike Montgomery, an astronomer at the University of Texas at Austin explained. “This is just circumstantial evidence, but maybe its internal structure isn’t what it would have been if it were a single star, and that’s somehow affecting its ability to pulsate.”

This is yet another display of Kepler’s prolific power of discovery, which can only mean that we can expect more and more discoveries of this type (and not only), and more mysteries await… just around the corner.