Tag Archives: binary system

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.”

Massive Black Hole Could Challenge Stellar Evolution Theories

Astronomers have used the Very Long Baseline Array (VLBA) to discover that the first black hole ever detected is actually much larger than previously believed. So large, at 21 times the mass of the Sun, that it challenges existing theories about the evolution of stars and how they form black holes. These constraints should limit stellar black holes in binary systems to about 15 solar masses.

Cygnus X-1 is a Milky Way binary system that contains a black hole and a supergiant companion star feeding it gas and other material. First discovered in 1964, the binary system has gone on to become one of the most intensely studied objects in astronomy. Yet, our familiarity with Cygnus X-1 doesn’t mean it can’t still deliver a surprise or two.

An artist’s impression of the Cygnus X-1 system. A stellar-mass black hole orbits with a
companion star located 7,200 light-years from Earth. (ICRAR)

In addition to finding the black hole is 50% more massive than prior estimates, near 21 solar masses as opposed to 15 solar masses, the team also discovered that the companion star also has a greater mass than previous measurements had revealed. The system as a whole is 20% further away than previously calculated–7,200 light-years from Earth as opposed to 6,100 light-years.

“We know that Cygnus X-1 hosts a black hole that is 21 times the mass of the Sun. We also learned that the supergiant companion star in Cygnus X-1 is also more massive than we had thought, with a mass of about 40 times the mass of the Sun,” Professor James Miller-Jones, the International Centre for Radio Astronomy Research (ICRAR), Curtin University, Australia, tells ZME Science. “The revised masses and distances also lead to an updated orbital separation between the star and the black hole — they orbit each other at a separation of one-quarter the distance from the Earth to the Sun.”

Cygnus X-1: New findings show the binary system is more massive and further away than previous estimates implied. (ICRAR)

The finding, published in the latest edition of the journal Science, means that Cygnus X-1 contains the largest black hole created through the collapse of a star alone, that has ever been detected with traditional electromagnetic astronomy without the use of gravitational waves. Larger black holes do of course exist, but these are formed through other mechanisms such as mergers between smaller black holes after that initial stellar collapse.

Miller-Jones, the study’s lead researcher, goes on to explain that the team also learned that the black hole is spinning very rapidly , close to its maximum possible speed. 

“With all this new information, we were able to propose a likely scenario for how this system formed, which can explain its observed properties.”

Professor James Miller-Jones, ICRAR, Curtin University

The finding doesn’t conform to current theories about black hole formation and stellar development in binary systems as its mass is greater than the limit imposed on such an object. 

How Cygnus X-1 Challenges Theories of Stellar Evolution

The team chanced on their finding whilst conducting an ambitious project to observe Cygnus X-1 almost continuously over a full 5.6-day orbit with the network of radio telescopes that comprise VLBA and X-ray telescopes. The aim of the research was to better understand how gas being fed into a black hole from a binary partner via a spiraling accretion disc connects to powerful jets of material that launch out from near the central region at near light speed.

“We had not originally aimed to refine the distance and the mass of the black hole but realised that our data would allow us to do so, by accounting properly for the effects of the black hole orbit.  But there is still a wealth of data from this rich observing campaign that we are looking to analyse more fully.”

Professor James Miller-Jones, ICRAR, Curtin University

“Black holes form from the deaths of the most massive stars when they run out of fuel and gravity takes over,” says Miller-Jones. “The mass of the resulting black hole is set by the initial mass of the star from which it formed — which we call the progenitor star — the amount of mass that star lost in winds over its lifetime, and any interactions with a nearby companion star.” 

Miller-Jones continues, saying massive stars launch very powerful winds from their surfaces, which leads to significant mass loss over their few-million year lifetimes. Some of the later phases of star’s evolution have particularly strong winds — determined by the abundance of elements heavier than helium in the gas from which the star was formed. More heavy elements mean stronger winds, and ultimately, a less massive star immediately before gravitational collapse. 

While some stars can also lose further mass in supernova explosions as they collapse to form a black hole, the evidence suggests that in Cygnus X-1, there was no explosion, and the star collapsed directly into a black hole,” says Miller-Jones. “The stronger the stellar winds during the late evolutionary phases of the star, the less massive we would have expected the black hole to be.”

An artist’s impression of the Cygnus X-1 system. This system contains the most massive stellar-mass black hole ever detected without the use of gravitational waves, weighing in at 21 times the mass of the Sun. (ICRAR)

At first, the team wasn’t totally aware of just how significant their discovery of mass disparities in the Cygnus X-1 binary system was. “I think that our biggest surprise was when we appreciated the full implications of our measurements,” Miller-Jones says. “As observational astronomers, my team and I had already found that we could revise the source distance and the black hole mass. However, it was not until I visited a colleague, Professor Ilya Mandel of Monash University, who is a theoretical astronomer, that we realised how important this actually was.”

Mandel–co-author on the resulting paper– realised that a 21-solar mass black hole was too massive to form in the Milky Way with the constraints in place due to the current prevailing estimates of the amount of mass lost by massive stars in stellar winds.

“The existence of such a massive black hole in our own Milky Way galaxy has shown us that the most massive stars blow less mass off their surface in winds than we had previously estimated. This improves our knowledge of how black holes form from the most massive stars.”

Professor James Miller-Jones, ICRAR, Curtin University

Cygnus X-1: No Stranger to Contraversy

The team’s findings have allowed them to put forward a scenario that would allow the formation of a 21 solar mass black hole in a binary system. “We suggest that the star that eventually collapsed into a black hole began its life a few million years ago with a mass of 55-75 times the mass of the Sun,” Miller-Jones tells ZME.  “Over its lifetime, it was close enough to its companion–the current supergiant–that gas from its surface was transferred onto its companion.  This removed the outer layers of the black hole progenitor and caused it to rotate more rapidly because the two stars were always keeping the same face towards one another. 

“Eventually, possibly as recently as a few tens of thousands of years ago the progenitor star collapsed directly into a black hole–of close to its current mass of 21 times the mass of the Sun–without a supernova explosion.”

Professor James Miller-Jones, ICRAR, Curtin University



Additionally, as well as gaining an insight into the black hole’s birth, Miller-Jones believes the team’s results could also indicate how the system could end its life. “Finally, we considered the eventual fate of this system,” the paper’s lead author says. “While the current companion star may eventually form a black hole, the separation of the two stars is such that the two black holes are unlikely to merge on a timescale comparable to the age of the Universe.”   

A companion paper appearing at the same time in the Astrophysical Journal will delve deeper into these elements of the research.

A closer look at the massive star in the Cygnus X-1 binary (ICRAR)

This isn’t the first time that Cygnus X-1, and more specifically its black hole, has sparked discussion in the fields of astronomy and cosmology. As speculation grew during that the intense X-ray source in the region was the result of a black hole, renowned physicist Stephen Hawking bet fellow scientist Kip Thorne–well known for his black hole work–in 1974 that Cygnus X-1 did not contain a black hole.

“This was a form of insurance policy for me. I have done a lot of work on black holes, and it would all be wasted if it turned out that black holes do not exist. But in that case, I would have the consolation of winning my bet, which would win me four years of the magazine Private Eye. If black holes do exist, Kip will get one year of Penthouse.”

Stephen Hawking, A Brief History of Time

Hawking lost the bet, conceding by breaking into Thorne’s office whilst he was on a trip to Russia and signing the framed bet.

The team now intend to apply the technique that led them to this finding to investigate further black holes. This should enable them to better understand how massive stars lose mass through stellar winds. With that said, as Cygnus X-1 is relatively unique in the Milky Way–as one of the few black holes so far detected in orbit with a massive companion star– Miller-Jones believes that they are unlikely to find any more binary systems in which the masses of the constituent star and black hole diverge so drastically from current estimates.

“Most excitingly for me, the advent of cutting-edge new telescopes such as the Square Kilometre Array radio telescope (SKA) will allow us to detect many more black holes, and study their properties, including how matter flows into and away from them, in more detail than ever before,” concludes Professor Miller-Jones. “It’s an exciting time to be in this field!”

Sources

Miller-Jones. J., Orosz. J. A., Mandel. I., ‘Cygnus X-1 contains a 21-solar mass black hole – implications for massive star winds,’ Science, [2021], [https://science.sciencemag.org/lookup/doi/10.1126/science.abb3363]

Astronomers find two failed stars wandering the universe together

A team of researchers from the University of Bern has discovered a very different binary system 450 light-years from Earth. The system — CFHTWIR-Oph 98 or Oph 98 for short — has twin occupants that appeared at first sight to be exoplanets existing in a star-less system. A deeper examination has revealed that they are brown dwarfs — Oph 98 A and Oph 98 B respectively — astronomical objects that are similar to stars but smaller and cooler.

This artist’s illustration represents a couple of planetary-mass brown dwarfs Ophiuchus 98. As they are very young, they are still evolving in the molecular clouds that saw their birth. (University of Bern, Illustration: Thibaut Roger)

These brown dwarfs wander the galaxy together, orbiting each other at an incredibly large distance equivalent to 200 times the distance between Earth and the Sun.

The discovery of the curious Oph 98 system by the research team led by Clémence Fontanive from the Center for Space and Habitability (CSH) and National Centre of Competence in Research PlanetS (NCCR PlanetS) is documented in a paper published in The Astrophysical Journal Letters.

A Star that Failed

The Oph 98 is a relativity new-born system in astrophysical terms, forming just 3 million years ago in the Ophiuchus stellar nursery (hence the ‘Oph’ element of its name). Its relative youth has some interesting consequences for the bodies that comprise it and led the team to properly identify its constituent bodies. 

The system has not existed for long enough for it to start forming planets. This means that Oph 98 A and B must have both formed via the same mechanisms that give rise to stars. This conclusion is also supported by the fact that Oph 98 B is roughly the right size to be a planet, but Oph A is too small to have the reservoir of material needed to form a planet so large. That means they must be brown dwarfs.

“This tells us that Oph 98 B, like its host, must have formed through the same mechanisms that produce stars and shows that the processes that create binary stars operate on scaled-down versions all the way down to these planetary masses,” says Fontanive.

In terms of mass brown dwarfs exist between planets and stars (NASA/ Caltech/ R. Hurt (IPAC).)

The fact that brown dwarfs form in ways that are similar to stars and share similar masses, but do not ignite with the nuclear processes that power stars, has often led to them being nicknamed ‘failed stars.’ It is extremely rare for star-forming processes to create worlds that go on to exist in a system such as this. 

The objects are rare examples of astronomical bodies similar to giant exoplanets that orbit each other without a parent star. Both are young brown dwarfs, with Oph 98 A being the larger of the two with a mass 15 times that of Jupiter. Its smaller companion — Oph 98 B — has a mass equivalent to 8 times that of the gas giant, which is the largest body other than the Sun in our solar system.

This isn’t the only thing that makes Oph 98 unique, however. 

Brown Dwarfs with a Weak Bond

Another thing that makes the Oph 98 system so remarkable is the fact that, like all binary systems, the bodies are gravitationally bound. These bonds are greater with objects of greater mass but follow an inverse square law — meaning the bond’s strength falls off quickly as separation distances increase. Because these objects have relatively small mass coupled with an extremely large separation, the gravitational bond between them is one of the weakest in terms of energy that astronomers have ever observed. 

Observing this system at all is no mean feat as brown dwarfs — especially low-mass ones — emit very little electromagnetic radiation and are thus, not easy to spot.

“Low-mass brown dwarfs are very cold and emit very little light, only through infrared thermal radiation,” explains Fontanive. “This heat glow is extremely faint and red, and brown dwarfs are hence only visible in infrared light.” 

The Ophiuchus cluster that is home to Oph 98 sits in a cloud of dust that makes it difficult to see. In this image it is pictured in X-rays by the Chandra X-Ray Observatory (Chandra X-Ray Observatory)

This visibility challenge was further compounded by the fact that Oph 98 and the Ophiuchus galaxy cluster itself is embedded in a dense cloud of dust that scatters visible light. “Infrared observations are the only way to see through this dust,” the researcher adds.

In fact, the team’s discovery was only made possible by the impressive power of the Hubble Space Telescope and the fact that it makes its observations from above Earth.

Hubble Shines Through Again

The Hubble Space Telescope is one of the only telescopes capable of observing objects as faint as the Oph 98 A and B and resolving the image of the brown dwarfs at such tight angles.

“Detecting a system like Oph 98 also requires a camera with a very high resolution, as the angle separating Oph 98 A and B is a thousand times smaller than the size of the moon in the sky,” Fontanive continues. 

The Hubble Space telescope’s vantage point above Earth’s atmosphere allows it to spot water vapor from brown dwarfs (ESA)

Hubble’s space-based vantage point is also crucial for the observation of such objects. This is because the infrared signatures that are used to observe brown dwarfs arise from water vapors that form in their upper atmospheres. As Earth’s atmosphere is full of water also producing this signal, the fainter trace from distant brown dwarfs is almost always obscured beyond detection for telescopes at the planet’s surface. 

“Both objects looked very red and showed clear signs of water molecules. This immediately confirmed that the faint source we saw next to Oph 98 A was very likely to also be a cold brown dwarf, rather than a random star that happened to be aligned with the brown dwarf in the sky,” says Fontanive.

The team also found Oph 98 in data collected by the CFHT (pictured) 14 years ago. (CFHT)

Interestingly, the team’s findings have helped confirm the fact that the Oph 98 system has actually been spotted before. The binary was also visible in data collected by the Canada-France-Hawaii Telescope (CFHT), located atop the summit of Mauna Kea, Hawaii, 14 years ago. This older data helped the team confirm how Oph 98 A and B move together across the galaxy as a pair.

“We observed the system again this summer from another Hawaiian observatory, the United Kingdom Infra-Red Telescope. Using these data, we were able to confirm that Oph 98 A and B are moving together across the sky over time, relative to other stars located behind them, which is evidence that they are bound to each other in a binary pair”, explains Fontanive. “We are really witnessing an incredibly rare output of stellar formation processes.”

Original Research

Fontanive. C., et al, ‘A wide planetary-mass companion to a young low-mass brown dwarf in Ophiuchus,’ The Astrophysical Journal Letters, [2020], [https://arxiv.org/abs/2011.08871]

Artist impression of the disc of dust and gas surrounding the massive protostar MM 1a, with its companion MM 1b forming in the outer regions. Credit: J. D. Ilee / University of Leeds.

This star is so massive it’s forming another star instead of planets

Artist impression of the disc of dust and gas surrounding the massive protostar MM 1a, with its companion MM 1b forming in the outer regions. Credit: J. D. Ilee / University of Leeds.

Artist impression of the disc of dust and gas surrounding the massive protostar MM 1a, with its companion MM 1b forming in the outer regions. Credit: J. D. Ilee / University of Leeds.

When astronomers cast their telescope towards an infant star, they were surprised to find that it was nursing a smaller stellar companion within its massive stellar disk. The amazing discovery marks the first time scientists have observed a star forming out of the fragmented disk of another.

Mega star and mini star

Some solar systems have two stars — they generally have a common center of gravity around which planets, asteroids, and other celestial bodies orbit. Such binary systems are quite common in the universe and astronomers believe that they usually form from the same molecular cloud.

Once a star or binary system settles, it starts forming planets out of the dense disk of gas and dust that surrounds them. Imagine the surprise of astronomers from the University of Leeds when they zoomed in on a young star called MM 1a and found a much smaller star, MM1b, lurking in the outer accretion disk where planets should normally form.

“Stars form within large clouds of gas and dust in interstellar space,” said Dr. Ilee, from the School of Physics and Astronomy at Leeds, said in a statement.

“When these clouds collapse under gravity, they begin to rotate faster, forming a disc around them. In low mass stars like our Sun, it is in these discs that planets can form.”

“In this case, the star and disc we have observed is so massive that, rather than witnessing a planet forming in the disc, we are seeing another star being born.”

The astronomers used turned to the Atacama Large Millimetre/submillimetre Array (ALMA), nested atop the Chilean desert, to spot the unusual stellar pairing. This unique instrument exploits a phenomenon called interferometry which enables 66 individual dishes to mimic the power of a single telescope with a theoretical diameter of 4 kilometers.

Credit: J. D. Ilee / University of Leeds.

The researchers were able to calculate the mass of both stars by measuring the amount of radiation emitted by the fragmented disk, as well as the very subtle shifts in the frequency of light emitted by disk’s gas. They found that MM 1a is 40 times more massive than the Sun while its companion star, MM 1b, weighs less than half the mass of the Sun.

Binary stars are often very similar in mass, meaning they likely formed as siblings. In this particular case, the mass ratio of the two stars is 80 to 1, clearly suggesting an entirely different process of formation for the two cosmic objects.

The British researchers came to the conclusion that the most favorable formation process for MM1b is in the outer regions of the massive accretion disk. In this outmost region, the disk can be gravitationally unstable, thereby collapsing under its own weight, forming a new star.

What’s more, the researchers believe that the small, young star could be surrounded by an accretion disk, which could lead to the formation of planets of its own. That’s a hypothesis that will need to be verified by subsequent observations. But even if such planets are in the process of forming or already exist, they’ll be shortlived.

 “Stars as massive as MM 1a only live for around a million years before exploding as powerful supernovae, so while MM 1b may have the potential to form its own planetary system in the future, it won’t be around for long,” Dr. Ilee said.

The rare binary system was described in the Astrophysical Journal Letters.

Artist's impression of 288P.

Hubble snaps the first binary-asteroid comet we’ve ever seen

Is it an asteroid? Is it a comet? It’s both and more. A group of astronomers recently published a paper describing one of the more unusual objects hidden in the asteroid belt. Known as 288P, this asteroid couple orbits each other while also exhibiting comet-like features.

Artist's impression of 288P.

Artist’s impression of 288P.
Image credits ESA / Hubble Images and Videos.

Back in September 2016, 288P was making its closest recorded approach to the Sun. Scientists naturally giggled in anticipation, since 288P looked like a comet and we don’t get to see belt-borne comets in this corner of space very often. Understanding how they form and behave could help teach us about the birth of the Solar System at large. So drawing on the NASA/ESA Hubble Space Telescope, the group of astronomers, led by Max Planck Institute for Solar System Research scientist Jessica Agarwal, seized this opportunity to take a detailed look at the body.

What they found is so far unique: 288P is not a single body, but two asteroids orbiting each other and exhibiting comet-like features, including a bright coma and a long tail. It is the first time we’ve even seen a binary asteroid body that’s also a comet.

Asteroids cometh

The snaps Hubble took of 288P showed that it’s actually a duo of asteroids, of almost the same size and mass, orbiting at about 100 kilometers (62.1 miles) from one another. This observation was crucial in itself, as by recording their orbits the team could calculate their masses. However, the data Hubble recorded also helped reveal ongoing activity in the binary system, the team reports, offering a glimpse of the body’s past.

“We detected strong indications of the sublimation of water ice due to the increased solar heating — similar to how the tail of a comet is created,” Agarwal explains.

“Surface ice cannot survive in the asteroid belt for the age of the Solar System but can be protected for billions of years by a refractory dust mantle, only a few metres thick.”

Starting from this, the team concluded that 288P has been in its current binary form for about 5,000 years now. The most probable cause of formation is “a breakup due to fast rotation,” Agarwal says, with the resulting fragments possibly being pushed further apart by “sublimation torques.” Binary asteroid systems are relatively common, but 288P stands out through the wide berth between the two component bodies, their near-equal size and mass, high eccentricity, and comet-like features, making 288P unique among known asteroid binaries in the Solar System.

One of the questions scientists are trying to answer when looking at main-belt bodies (comets as well as asteroids) is whether or not they shuttled water from space to young Earth, helping create the oceans of today. We don’t get to see a lot of them up close, so 288P stands out as an extremely important system for future studies. Its uniqueness also poses some problems, however. It’s so starkly different from anything else we’ve seen that we don’t have anything to meaningfully compare it with — so we don’t know if its properties are a fluke or quite common.

“We need more theoretical and observational work, as well as more objects similar to 288P, to find an answer to this question,” concludes Agarwal.

Since snapping 288P involved quite a bit of luck, it may be quite a while before we spot these objects, though.

The paper “A binary main belt comet” has been published on ESA’s hubblesite, here.

The center of the Milky Way galaxy, with the supermassive black hole Sagittarius A* (Sgr A*), located in the middle, is revealed in these images. The large image contains X-rays from Chandra in blue and infrared emission from the Hubble Space Telescope in red and yellow. Credit: NASA

Mysterious object at the heart of Milky Way might be a Merged Star

A mysterious cosmic object thought to be an immense cloud of gas and dust left scientists scratching their heads after it wasn’t consumed by the supermassive black hole that lies at the center of our galaxy. After it passed a critical point in its orbit around the black hole – where a gas cloud would have typically become engulfed in a fireworks show – followup analysis suggests that the object, dubbed G2, is actually binary system (a solar system with two stars) which has merged into a bright, mega star following the close encounter.

More than the black hole could chew

The center of the Milky Way galaxy, with the supermassive black hole Sagittarius A* (Sgr A*), located in the middle, is revealed in these images. The large image contains X-rays from Chandra in blue and infrared emission from the Hubble Space Telescope in red and yellow.  Credit: NASA

The center of the Milky Way galaxy, with the supermassive black hole Sagittarius A* (Sgr A*), located in the middle, is revealed in these images. The large image contains X-rays from Chandra in blue and infrared emission from the Hubble Space Telescope in red and yellow. Credit: NASA

The object was first identified in 2011, and astronomers had been excited ever since in anticipation of the moment it would become consumed by Sagittarius A*, the supermassive black hole at the Milky Way’s center. This should have happened by July of this year, but strangely enough the event didn’t unfold as predicted. If G2 was indeed a gas cloud, then the dynamics surrounding the black hole’s event horizon would have pulled in clumps of gas and dust, generating powerful flares. Instead, astronomers studying the object using the European Southern Observatory’s Very Large Telescope in Chile found that these effects were a lot milder and subtle.

The G2 object, captioned in the middle of the image snapped by the Keck telescopes shortly after its close encounter with a supermassive black hole. Credit: ANDREA GHEZ, GUNTHER WITZEL/UCLA GALACTIC CENTER GROUP/W. M. KECK OBSERVATORY

The G2 object, captioned in the middle of the image snapped by the Keck telescopes shortly after its close encounter with a supermassive black hole. Credit: ANDREA GHEZ, GUNTHER WITZEL/UCLA GALACTIC CENTER GROUP/W. M. KECK OBSERVATORY

A team led by Andrea Ghez of the University of California, Los Angeles, followed-up using the twin 10-meter Keck telescopes in Hawaii to observe G2 between March and August which peered through the avalanche of gas and dust at 3 micrometer infrared wavelengths. The researchers found the object survived the close encounter and was back to its usual orbit.

“G2 survived and continued happily on its orbit; a simple gas cloud would not have done that,” said Ghez. “G2 was basically unaffected by the black hole. There were no fireworks.”

Instead, what Ghez and colleagues discovered was that the mysterious object is in fact a star surrounded by a gas and dust envelope, hence the confusion the researchers argue. This is not an ordinary star, and its close encounter with Sagittarius certainly didn’t leave G2 unscathed. Apparently, G2 was initially a binary system – two stars tugged together by gravity. Binary systems are very common throughout the galaxy, and systems comprised of three or more stars are also possible.

The star is twice the mass of our sun but 100 times its size, the team reports this week in The Astrophysical Journal Letters. It makes sense since the binary stars merged together following a spirally trajectory influenced by the black hole’s gravity.  The result is a new star so hot that it swells up like a freshly ignited young protostar. If this hypothesis is true, then astronomers might now be able to understand and unravel other mysteries surrounding  Sagittarius A* like why there’s an unusual amount of young stars in the black hole’s neighborhood, but almost no old stars.

“This may be happening more than we thought. The stars at the center of the galaxy are massive and mostly binaries,” said Ghez. “It’s possible that many of the stars we’ve been watching and not understanding may be the end product of mergers that are calm now.”

“We are seeing phenomena about black holes that you can’t watch anywhere else in the universe,” added Ghez. “We are starting to understand the physics of black holes in a way that has never been possible before.”

his artist's impression shows the dust and gas around the double star system GG Tauri-A. Credit: ESO/L.Calçada

A ‘Ying Yang’ binary system that can sustain Planetary Formation

A group from the Laboratory of Astrophysics of Bordeaux, France, and the National Centre for Scientific Research (CNRS) has made a most exciting discovery. The astronomers found that an odd binary system – a solar system comprised of two stars – actually behaves like a double star, with two disks of matter encircling the system in a beautiful dance of gas and dust exchange. The breakthrough came after observations showed that that two disks – a wheel inside a wheel –  transfer matter from the outside to the inside, thus sustaining the smaller disk and aiding in planetary formation. The discovery has profound implications in exoplanet search efforts.

Two solar wheels

his artist's impression shows the dust and gas around the double star system GG Tauri-A.  Credit: ESO/L.Calçada

his artist’s impression shows the dust and gas around the double star system GG Tauri-A. Credit: ESO/L.Calçada

The outer disk surrounds the entire system, called GG Tau-A, while the inner disk circles the two companion stars closely. The latter disk has a mass roughly equivalent to that of Jupiter, yet it’s existence has perplexed scientists for quite a while. The two stars are constantly feeding matter from the disk, so in time it should have disappeared – why are we still seeing it? Using the  Atacama Large Millimeter/submillimeter Array (ALMA) in Chile,  Anne Dutrey and colleagues found gas clumps in the region between the two disks, which serves to explain the anomaly since it means matter is being transferred from the outer ring to the inner one, thus sustaining it.

“Material flowing through the cavity was predicted by computer simulations but never imaged before. Detecting these clumps indicates that material is moving between the disks, allowing one to feed off the other,” said Anne Dutrey from the Laboratory of Astrophysics, Bordeaux in France.

[RELATED] Most powerful stars are actually vampire binary systems

New planetary formation insight

Artist’s concept of exoplanets in a two-stars system. The planets found so far orbiting such systems are gas giants like Jupiter. Credit: NASA/JPL-Caltech/T. Pyle

Artist’s concept of exoplanets in a two-stars system. The planets found so far orbiting such systems are gas giants like Jupiter. Credit: NASA/JPL-Caltech/T. Pyle

This is where things get interesting. Planets are born from the same spinning disk of gas and dust material that went into forming a star, like our sun. This disk is called a solar nebula and even after some of this material was bound by gravity and collapsed to form a star, it still retains an angular momentum while it orbits the new-born star. Particles in the spinning disc begin to clump together as gravity attracted them to each other and over millions of years these clumps continue to collide and join together, in a process which scientists described as accretion. Because this is an extremely enduring and slow process, the solar nebula needs to have enough material to feed the planetary formation, as well as parent star which also sucks in gas and dust from the disk.

“We may be witnessing these types of exoplanetary systems in the midst of formation,” said Jeffrey Bary, an astronomer at Colgate University in Hamilton, N.Y., and co-author of the paper. “In a sense, we are learning why these seemingly strange systems exist.”

Artist's conception of the Kepler-35 system. Credit: Lynette Cook / extrasolar.spaceart.org / Nature

Artist’s conception of the Kepler-35 system. Credit: Lynette Cook / extrasolar.spaceart.org / Nature

If the same process occurs in binary systems such as GG Tau-A, then it would explain why so many planets have been and continue to be discovered in binary systems. Originally, scientists weren’t interested in binary systems when looking for planets outside our solar system, but now investigators are beginning to take an even closer look and investigate the possibility of planets orbiting individual stars of multiple-star systems.

“This means that multiple star systems have a way to form planets, despite their complicated dynamics. Given that we continue to find interesting planetary systems, our observations provide a glimpse of the mechanisms that enable such systems to form,” concludes Bary.

GG Tau-A  is only a few million years old and lies approximately 460 light-years from Earth in the constellation Taurus. The discovery was reported in the journal Nature.

Scientists find double supermassive black hole

Astronomers have for the first time discovered a pair of supermassive black holes that orbit each other in an ordinary galaxy.

At the heart of most galaxies, there lies a supermassive black hole – as you probably already figured out from the name, it’s like a normal black hole, but much bigger. But two supermassive black holes? That’s a smoking gun – a clear indication that the galaxy in which they are located is in fact the result of a collision between two galaxies.

As you might guess, these collisions are not particularly frequent. Up to date, only a few candidates for such binary black hole systems have been located, by studying X-rays emitted by the galaxies’ centers. In the process of galactic collision, the gas is heated so much that it shines at many wavelengths, including X-rays. This gives the galaxy an unusually bright center, and leads to it being called active.

Four years ago, on June 2010, Dr Fukun Liu from Peking University in China with colleagues spotted a tidal disruption event in the galaxy SDSS J120136.02+300305.5 (J120136 for short). They were specifically looking for this kind of events, and, lo and behold, they got lucky.

The galaxy they were looking at was spilling massive amounts of X-rays, which they detected. It looked exactly like the signature of a supermassive black hole, but as they continued to track it, they noticed something strange – the intensity was dropping more and more. After 48 days, they started reemerging, just as if nothing happened.

“This is exactly what you would expect from a pair of supermassive black holes orbiting one another,” said Dr Liu, who is the lead author of the study published in the Astrophysical Journal (also on arXiv.org).

Image via Scientific American.

They constructed models to see what the possible configurations are, and they found that there are two possible solutions to this system: either the primary black hole “weighs” 10 million solar masses and is orbited by a black hole of about a million solar masses in an elliptical orbit, or the primary black hole is about a million solar masses and is orbited in a circular orbit. In either case, the distance between the two holes is really small – comparable to our solar system.

Judging by this small distance, it’s very likely that the two will merge sooner or later. What happens when two supermassive black holes collide? Well, to cut a long story short, you end up with one, super supermassive black hole. This study could provide valuable information about the way galaxies merge, and what is left in the aftermath.

“Once we have detected thousands of tidal disruption events, we can begin to extract reliable statistics about the rate at which galaxies merge,” said study co-author Dr Stefanie Komossa of the Max-Planck-Institut für Radioastronomie in Bonn, Germany.

N. Farsad et al./PLOS ONE

Sending a text message using Vodka molecules – the first continuous molecular communication

In nature, organisms communicate in various ways, be it through acoustic or biological signals. Insects, for instance, communicate and relay important information, such as a threat to a hive, using pheromones – an excreted chemical with a particular signature. Scientists at the University of Warwick in the UK and the York University in Canada have created a molecular communications system which they used to send a continuous signal, like a text message, just by spraying alcohol molecules. The system in a more advanced form could facilitate communication in environments where electromagnetic waves can’t be used, like through pipelines or oil rigs.

N. Farsad et al./PLOS ONE

N. Farsad et al./PLOS ONE

Previous attempts also relayed information using molecular signaling, however this is the first time continuous data transmission has been achieved. Moreover, the system was built using off-the shelf components with an overall cost that doesn’t exceed $100.

Molecular receiver: one of three sensors (for various types of tests) demodulates the incoming signal by assigning the bit 1 to increasing concentration and 0 to decreasing. The binary data is converted back to letters in the Arduino board and sent via serial port to a computer for display. (Credit: N. Farsad et al./PLOS ONE)

Molecular receiver: one of three sensors (for various types of tests) demodulates the incoming signal by assigning the bit 1 to increasing concentration and 0 to decreasing. The binary data is converted back to letters in the Arduino board and sent via serial port to a computer for display. (Credit: N. Farsad et al./PLOS ONE)

The message is inputted through an LCD Shield Kit then encoded by an Arduino board as a binary sequence – 1 corresponds to higher concentration of molecules, while 0 to lower concentration. In their demonstration, the researchers programmed a sprayer to release evaporated alcohol molecules several meters across open space before it was decoded by a receiver. The message was “O Canada” – a tribute to the Canadian national anthem.

A sprayed text message

“We believe we have sent the world’s first text message to be transmitted entirely with molecular communication, controlling concentration levels of the alcohol molecules, to encode the alphabets with single spray representing bit 1 and no spray representing the bit 0,” said York doctoral candidate Nariman Farsad, who led the experiment.

“Imagine sending a detailed message using perfume — it sounds like something from a spy thriller novel, but in reality it is an incredibly simple way to communicate,” said Dr. Weisi Guo from the School of Engineering at the University of Warwick.

“Of course, signaling or cues are something we see all the time in the natural world — bees for example use chemicals in pheromones to signal to others when there is a threat to the hive, and people have achieved short-range signaling using chemicals.

“But we have gone to the next level and successfully communicated continuous and generic messages over several meters.

The system could find potential use in medicine. Recent advancements have allowed nanoscale devices to be embedded into organs, for instance, where they sense and gather important data. In this tiny environment, however, there are some constraints to using electromagnetic waves to propagate information – after all an antenna can only be so small. Chemical communication require very little energy, is bio-compatible and could thus provide the means to solve this problem.

A more immediate practical application, however, may be seen in places like pipe lines, sewers or oil rigs. The molecular communication system could be used here to send important safety information and advert potentially catastrophic accidents.

The system was described in a paper published in the journal PLOS ONE.

Vampire Star

Most powerful stars are actually vampire binary systems. The weaker feeds on the stronger

Vampire StarA new research has found that the massively powerful O-type stars, which can be up to 90 times more powerful than our own sun, actually come in pairs most of the time, as a binary system. The two stars wrapper in this dance have a special kind of relationship developed with one another. Thus, one of the stars feeds on the other, sucking gas and fuel from its counterpart like a vampire, or the two eventually end up merging into a single star.

Astronomers used the European Southern Observatory’s Very Large Telescope in Chile to study the  massive O-type stars – incredibly hot and intensely bright stars.

“These stars are absolute behemoths,” says Hugues Sana of the University of Amsterdam.

“They have 15 or more times the mass of our sun and can be up to a million times brighter. These stars are so hot that they shine with a brilliant blue-white light and have surface temperatures over 30,000 degrees Celsius.”

Data gathered from the light  captured by the telescope and  emitted by 71 O-type single stars and members of binaries in six nearby young star clusters in the Milky Way bewildered scientists. According to their findings, 75 percent of all O-type stars exist as part of binary systems, a higher proportion than previously thought.

Type O stars are important for the Universe’s “ecosystem” and represent one of the most powerful classes of stars known in the cosmos. They drive galaxy evolution by hurling heavy elements crucial for life through space via the powerful winds and shocks coming from the stars. Also, they’re associated with with gamma-ray bursts, which are among the most energetic phenomena in the Universe. But these stellar giants can also exhibit extreme behavior, garnering the nickname ” vampire stars ” for the way they suck matter from neighboring companions.

“The life of a star is greatly affected if it exists alongside another star,” says Selma de Mink of the Space Telescope Science Institute.

“If two stars orbit very close to each other they may eventually merge. But even if they don’t, one star will often pull matter off the surface of its neighbour.”

Until now, most astronomers believed that closely-orbiting massive binary stars were rare. This isn’t the case as this recent study found. On the contrary heavyweight double stars are rather common it seems, and their life cycle greatly differs from those of single stars. In the case of vampire stars, the lower-mass star sucks fresh hydrogen from its companion, substantially increasing its mass and enabling it to live much longer than a single star of the same mass would. The victim star, on the other hand, is left with an exposed core that mimics the appearance of a much younger star. This might mislead some scientists in their efforts, the researchers worry.

“The only information astronomers have on distant galaxies is from the light that reaches our telescopes,” says Sana.

“Without making assumptions about what is responsible for this light we cannot draw conclusions about the galaxy, such as how massive or how young it is. This study shows that the frequent assumption that most stars are single can lead to the wrong conclusions.”

Findings were reported in Friday’s issue of the journal Science.

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