A Recently Discovered Double Binary System is Unstable. Stars Could Collide, Leading to a Supernova

Artist view of a close orbiting binary star. Credit: ESO/L. Calçada

Multiple star systems are very common in the Milky Way. While most of these systems are binary systems consisting of two stars, others contain three, four, or even six stars. These systems tend to be pretty stable since unstable systems tend to break apart or merge fairly quickly, but sometimes you can get a kind of meta-stable system. One that lasts long enough for stars to evolve while still being stable in the end. And that end could be a supernova.

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Slimmed Down Red Giants Had Their Mass Stolen By a Companion Star

Millions of stars that can grow up to 620 million miles in diameter, known as ‘red giants,’ exist in our galaxy, but it has been speculated for a while that there are some that are possibly much smaller. Now a team of astronomers at the University of Sydney have discovered several in this category and have published their findings in the journal Nature Astronomy.

“It’s like finding Wally… we were extremely lucky to find about 40 slimmer red giants, hidden in a sea of normal ones. The slimmer red giants are either smaller in size or less massive than normal red giants.”

PhD candidate Mr Yaguang Li from the University of Sydney, as quoted from the source article.
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This is how you get Tatooines. Binary Star Planet Formation

One of the less appreciated aspects of George Lucas’ vision for Star Wars was that he predicted the existence of planets in binary star systems years before we saw even the first exoplanet.  Now a team from the University of Cambridge and the Max Planck Institute for Extra-terrestrial Physics have found how exactly those planets can form without being torn apart by their accompanying suns.

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A Nearby White Dwarf Might be About to Collapse Into a Neutron Star

Credit: Giuseppe Parisi

About 97% of all stars in our Universe are destined to end their lives as white dwarf stars, which represents the final stage in their evolution. Like neutron stars, white dwarfs form after stars have exhausted their nuclear fuel and undergo gravitational collapse, shedding their outer layers to become super-compact stellar remnants. This will be the fate of our Sun billions of years from now, which will swell up to become a red giant before losing its outer layers.

Unlike neutron stars, which result from more massive stars, white dwarfs were once about eight times the mass of our Sun or lighter. For scientists, the density and gravitational force of these objects is an opportunity to study the laws of physics under some of the most extreme conditions imaginable. According to new research led by researchers from Caltech, one such object has been found that is both the smallest and most massive white dwarf ever seen.

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There are Natural Starshades Out There, Which Would Help Astronomers Image Exoplanets

TOI 1338 b is a circumbinary planet orbiting its two stars. It was discovered by TESS. Image Credit: NASA's Goddard Space Flight Center/Chris Smith

In the past few decades, the study of extrasolar planets has grown by leaps and bounds, with the confirmation of over 4000 exoplanets. With so many planets available for study, the focus of exoplanet-researchers is shifting from discovery to characterization. In the coming years, new technologies and next-generation telescopes will also enable Direct Imaging studies, which will vastly improve our understanding of exoplanet atmospheres.

To facilitate this process, astronomers will rely on costly technologies like coronagraphs and starshades, which block out the light of a star so any planets orbiting it will become more visible. However, according to a new study by an international team of astronomers and cosmologists, eclipsing binary stars could provide all the shading that’s needed to directly image planets orbiting them.

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Of the Two Stars in Alpha Centauri, One is Probably More Habitable than the Other

Artist's impression of a hypothetical planet orbiting the star Alpha Centauri B, a member of the triple star system that is the closest to Earth. Credit: ESO

In the past, the number of known exoplanets has exploded, with 4093 confirmed detections so far (and another 4,727 candidates awaiting confirmation). With the discovery of so many planets that are dozens, hundreds, or even thousands of light years away, a great deal of attention has understandably been directed to our nearest stellar neighbors. Could planets be right next door, with the possibility of life being there as well?

While a potentially-habitable planet was recently discovered around Proxima Centauri (Proxima b), Alpha Centauri remains something of a question mark. But thanks to a recent study from the Georgia Institute of Technology (GIT), we might be getting closer to determining if this neighboring system supports life. In a twist, the study revealed that one of the stars in the binary system is more likely to be habitable than the other.

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An Extremely Rare Gamma Ray Emitting Neutron Star Binary Has Been Found

The Very Energetic Radiation Imaging Telescope Array System (VERITAS) at Fred Lawrence Whipple Observatory in southern Arizona. Credit: John Quinn/CfA

Neutron stars are one of the most fascinating astronomical objects in the known Universe. In addition to being the densest type of star (with the possible exception of quark stars), they have also been known to form binary pairs with massive stars. To date, only 39 such systems have been discovered, and even fewer have been detected that were composed of a massive star and a very high energy (VHE) gamma-ray neutron star.

To date, only two of these systems have been found, the second of which was discovered just a few years ago by a team of international astronomers known as the Very Energetic Radiation Imaging Telescope Array System (VERITAS) collaboration. In addition to being a rare find, the discovery was also very fortunate, since the unusual behavior they observed coming from this system will not be happening again until 2067.

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Globular Clusters Might not be as Old as Astronomers Thought. Like, Billions of Years Younger

A binary star system in a globular cluster. Credit: University of Warwick

Globular clusters have been a source of fascination ever since astronomers first observed them in the 17th century. These spherical collections of stars are among the oldest known stars in the Universe, and can be found in the outer regions of most galaxies. Because of their age and the fact that almost all larger galaxies appear to have them, their role in galactic evolution has remained something of a mystery.

Previously, astronomers were of the opinion that globular clusters were some of the earliest stars to have formed in the Universe, roughly 13 billion years ago. However, new research has indicated that these clusters may actually be about 4 billion years younger, being roughly 9 billion years old. These findings may alter our understanding of how the Milky Way and other galaxies formed, and how the Universe itself came to be.

The study, titled “Reevaluating Old Stellar Populations“, recently appeared online and is being evaluated for publication in The Monthly Notices for the Royal Astronomical Society. The study was led by Dr. Elizabeth Stanway, an Associate Professor in the Astronomy group at the University of Warwick, UK, and was assisted by Dr. J.J. Eldridge, a Senior Lecturer at the University of Auckland, New Zealand.

Within larger galaxies, like the Milky Way, globular clusters are part of the galactic halo. Between 150 and 180 are estimated to be part of the Milky Way alone. Credit: ESO

For the sake of their study, Dr. Stanway and Dr. Eldridge developed a series of new research models designed to reconsider the evolution of stars. These models, known as Binary Population and Spectral Synthesis (BPASS) models, had previously proven effective in exploring the properties of young stellar populations within the Milky Way and throughout the Universe.

Using these same models, Dr. Stanway and Dr. Eldridge studied a sample of globular clusters in the Milky Way and nearby quiescent galaxies. They also took into account the details of binary star evolution within globular clusters and used them to explore the colors of light and spectra from old binary populations. In short, binary star system evolution consists of one star expanding into a giant while the gravitational force of the smaller star strips away the atmosphere of the giant.

What they found was that these binary systems were about 9 billion years old. Since these stars are thought to have formed at the same time as the globular clusters themselves, this demonstrated that globular clusters are not as old as other models have suggested. As Dr. Stanway said of the BPASS models she and Dr. Eldridge developed:

“Determining ages for stars has always depended on comparing observations to the models which encapsulate our understanding of how stars form and evolve. That understanding has changed over time, and we have been increasingly aware of the effects of stellar multiplicity – the interactions between stars and their binary and tertiary companions.

An artist’s impression of a millisecond pulsar and its companion. The presence of binaries in globular clusters is a good means of providing age estimates of those clusters. Credit: ESA & Francesco Ferraro (Bologna Astronomical Observatory)

If correct, this study could open up new pathways of research into how massive galaxies and their stars are formed. However, Dr. Stanway admits that much work still lies ahead, which includes looking at nearby star systems where individual stars can be resolved – rather than considering the integrated light of a cluster. Nevertheless, the study could have immense significant for our understanding of how and when galaxies in our Universe formed.

“If true, it changes our picture of the early stages of galaxy evolution and where the stars that have ended up in today’s massive galaxies, such as the Milky Way, may have formed,” she said. “We aim to follow up this research in the future, exploring both improvements in modelling and the observable predictions which arise from them.”

An integral part of cosmology is understanding when the Universe came to be the way it is, not just how. By determining how old globular clusters are, astronomers will have another crucial piece of the puzzle as to how and when the earliest galaxies formed. And these, combined with observations that look to the earliest epochs of the Universe, could just yield a complete model of cosmology.

Further Reading: University of Warwick, arXiv

For the First Time, Astronomers Have Found a Star That Survived its Companion Exploding as Supernova

Hubble image of the supernova SN 2001ig, which indicated the presence of a companion. Credits: NASA, ESA, S. Ryder (Australian Astronomical Observatory), and O. Fox (STScI)

A Type II supernova is a truly amazing astronomical event. As with all supernovae, a Type II consists of a star experiencing core collapse at the end of its life cycle and exploding, causing it to shed its outer layers. A subclass of this type is known as Type IIb, which are stars that have been stripped of their hydrogen fuel and undergo collapse because they are no longer able to maintain fusion in their core.

Seventeen years ago, astronomers were fortunate enough to witness a Type IIb supernova in the galaxy NGC 7424, located 40 million light-years away in the southern constellation Grus. Now that this supernova has faded, the Hubble Space Telescope recently captured the first image of a surviving companion, thus demonstrating that supernovae do indeed happen in double-star systems.

The study, titled “Ultraviolet Detection of the Binary Companion to the Type IIb SN 2001ig“, was recently published in the Astrophysical Journal. The study was led by Stuart Ryder of the Australian Astronomical Observatory and included members from California Institute of Technology (Caltech), the Space Telescope Science Institute (STSI), the University of Amsterdam, the University of Arizona, the University of York, and the University of California.

This discovery is the most compelling evidence to date that some supernovae originate as a result of siphoning between binary pairs. As Stuart Ryder indicated in a recent NASA press release:

“We know that the majority of massive stars are in binary pairs. Many of these binary pairs will interact and transfer gas from one star to the other when their orbits bring them close together.”

The supernova, called SN 2001ig, was pinpointed by astronomers in 2002 using the European Southern Observatory’s Very Large Telescope (VLT). In 2004, these observations were followed-up with the Gemini South Observatory, which first hinted at the presence of a surviving binary companion. Knowing the exact coordinates, Ryder and his team were able to focus Hubble on that location as the supernova’s glow faded.

The find was especially fortuitous because it might also shed light on a astronomical mystery, which is how stripped-envelop supernovae lose their outer envelopes. Originally, scientists believed they were the result of stars with very fast winds that pushed off their outer envelopes. However, when astronomers began looking for the primary stars which spawned these supernovae, they could not find them.

Artist’s impression of a pulsar siphoning material from a companion star. Credit: NASA

As Ori Fox, a member of the Space Telescope Science Institute and a co-author on the paper, explained:

“That was especially bizarre, because astronomers expected that they would be the most massive and the brightest progenitor stars. Also, the sheer number of stripped-envelope supernovas is greater than predicted.”

This led scientists to theorize that many of the stripped-envelop stars were the primary in lower-mass binary star systems. All that remained was to find a supernova that was part of a binary system, which Ryder and his colleagues set out to do. This was no easy task, seeing as how the companion was rather faint and at the very limits of what Hubble could see.

In addition, not many supernovae are known to go off within this distance range. Last, but not least, they had to know the exact position through very precise measurements. Thanks to Hubble’s exquisite resolution and ultraviolet capability, they were able to find and photograph the surviving companion.

Prior to the supernova, the stars orbited each other with a period of about one year. When the primary star exploded, it had an impact on the companion, but it remained intact. Because of this, SN 2001ig is the first surviving companion to ever be photographed.

Artist’s rendering of SN 1993J, where a red supergiant supernova progenitor star (left) is exploding after having transferred about 10 solar masses of hydrogen gas to the blue companion star (right). Credit: ESA

Looking ahead, Ryder and his team hope to precisely determine how many supernovae with stripped envelopes have companions. At present, it is estimated that at least half of them do, while the other half lose their outer enveloped due to stellar winds. Their next goal is to examine completely stripped-envelope supernovae, as opposed to SN 2001ig and SN 1993J, which were only about 90% stripped.

Luckily, they won’t have to wait as long to examine these completely stripped-envelope supernovae, since they don’t have as much shock interaction with gas in their surrounding environment. In short, since they lost their outer envelopes long before they exploded, they fade much faster. This means that the team will only have to wait two to three years before looking for the surviving companions.

Their efforts are also likely to be helped by the deployment of the James Webb Space Telescope (JWST), which is scheduled to launch in 2020. Depending on what they find, astronomers may be ready to resolve the mystery of what causes the different types of supernovae, which could also reveal more about the life cycles of stars and the birth of black holes.

Further Reading: NASA, The Astrophysical Journal

That Interstellar Asteroid ‘Oumuamua Probably Came From a Binary Star System

Artist’s impression of the first interstellar asteroid/comet, "Oumuamua". This unique object was discovered on 19 October 2017 by the Pan-STARRS 1 telescope in Hawaii. Credit: ESO/M. Kornmesser

On October 19th, 2017, the Panoramic Survey Telescope and Rapid Response System-1 (Pan-STARRS-1) telescope in Hawaii announced the first-ever detection of an interstellar asteroid – I/2017 U1 (aka. ‘Oumuamua). Since that time, no effort has been spared to study this object before it leaves our Solar System. These include listening to it for signs of communications, determining its true nature and shape, and determining where it came from.

In fact, the question of this interstellar object’s origins has been mystery since it was first discovered. While astronomers are sure that it came from the direction of Vega and some details have been learned about its past, where it originated from remains unknown. But according to a new study by a team of astronomers from the University of Toronto, Scarborough, ‘Oumuamua may have originally come from a binary star system.

The study, titled “Ejection of rocky and icy material from binary star systems: Implications for the origin and composition of 1I/‘Oumuamua “, recently appeared in the Monthly Notices of the Royal Astronomical Society. The study was led by Alan P. Jackson, a research fellow at the Center for Planetary Sciences (CPS) at the University of Scarborough, and included members from both the CPS and the Canadian Institute for Theoretical Astrophysics (CITA).

Oumuamua as it appeared using the William Herschel Telescope on the night of October 29. Credit: Queen’s University Belfast/William Herschel Telescope

For the sake of their study, Jackson and his co-authors considered how in single star systems (like our own), asteroids do not get ejected very often. For the most part, it is comets that become interstellar objects, mainly because they orbit the Sun at a greater distance and are less tightly bound by its gravity. And while ‘Oumuamua was initially mistaken for a comet, follow-up observations by the European Southern Observatory (ESO) indicated that it is  likely an asteroid.

With the help of other astronomers, it soon became apparent that ‘Oumuamua was likely an oddly-shaped rocky object that measured about 400 meters (1312 ft) long and was tube-shaped. These findings were rather surprising to astronomers. As Jackson explained in a recent Royal Astronomical Society press release:

“It’s really odd that the first object we would see from outside our system would be an asteroid, because a comet would be a lot easier to spot and the Solar System ejects many more comets than asteroids.”

As such, Jackson and his team hypothesized that interstellar objects like ‘Oumuamau are more likely to be ejected from a binary system. To test this theory, they constructed a population synthesis model that considered just how common binary star systems are in the Galaxy. They also conducted 2000 N-body simulations to see just how efficient such systems would be at ejecting objects like ‘Oumuamua.

Diagram showing the orbit of the interstellar asteroid ‘Oumuamua as it passes through the Solar System. Credit: ESO/K. Meech et al.

What they found was that binary stars are produced at a rate of about 30% by number and 41% by mass, and that rocky objects like ‘Oumuamua are far more likely to be ejected from binary than single star systems. Based on ‘Oumuamua’s rocky composition, they also determined that the asteroid was likely ejected from the inner part of its solar system (i.e. inside the “Ice Line”) while the system was still in the process of formation.

Lastly, they determined that rocky objects are ejected from binary systems in comparable numbers to icy objects. This is based on the fact that the presence of a companion star would mean that more material would become unstable due to stellar encounters. In the end, this material would be more likely to be ejected rather than accreted to form planets, or take up residence in the outer reaches of the star system.

While there are still many unanswered questions about ‘Oumuamua, it remains the first interstellar asteroid that scientists have ever known. As such, its continued study can tell us a great deal about what lies beyond our Solar System. As Jackson put it:

“The same way we use comets to better understand planet formation in our own Solar System, maybe this curious object can tell us more about how planets form in other systems.”

The team’s findings were also the subject of a presentation that took place at the 49th Lunar and Planetary Science Conference, which took place this week at The Woodlands, Texas.

Further Reading: Royal Astronomical Society, MNRAS