New Study Says a Fast Radio Burst Happens Every Second in the Universe

When astronomers first noted the detection of a Fast Radio Burst (FRB) in 2007 (aka. the Lorimer Burst), they were both astounded and intrigued. This high-energy burst of radio pulses, which lasted only a few milliseconds, appeared to be coming from outside of our galaxy. Since that time, astronomers have found evidence of many FRBs in previously-recorded data, and are still speculating as to what causes them.

Thanks to subsequent discoveries and research, astronomers now know that FRBs are far more common than previously thought. In fact, according to a new study by a team of researchers from the Harvard-Smithsonian Center for Astrophysics (CfA), FRBs may occur once every second within the observable Universe. If true, FRBs could be a powerful tool for researching the origins and evolution of the cosmos.

The study, titled “A Fast Radio Burst Occurs Every Second throughout the Observable Universe“, recently appeared in The Astrophysical Journal Letters. The study was led by Anastasia Fialkov, a postdoc researcher and Fellow at the CfA’s Institute for Theory and Computation (ITC). She was joined by Professor Abraham Loeb, the director of the ITC and the Frank B. Baird, Jr. Professor of Science at Harvard.

As noted, FRBs have remained something of a mystery since they were first discovered. Not only do their causes remain unknown, but much about their true nature is still not understood. As Dr. Fialkov told Universe Today via email:

“FRBs (or fast radio bursts) are astrophysical signals of an undetermined nature. The observed bursts are short (or millisecond duration), bright pulses in the radio part of the electromagnetic spectrum (at GHz frequencies). Only 24 bursts have been observed so far and we still do not know for sure which physical processes trigger them. The most plausible explanation is that they are launched by rotating magnetized neutron stars. However, this theory is to be confirmed.”

For the sake of their study, Fialkov and Loeb relied on observations made by multiple telescopes of the repeating fast radio burst known as FRB 121102. This FRB was first observed in 2012 by researchers using the Arecibo radio telescope in Puerto Rico, and has since been confirmed to be coming from a galaxy located 3 billion light years away in the direction of the Auriga constellation.

Since it was discovered, additional bursts have been detected coming from its location, making FRB 121102 the only known example of a repeating FRB. This repetitive nature has also allowed astronomers to conduct more detailed studies of it than any other FRB. As Prof. Loeb told Universe Today via email, these and other reasons made it an ideal target for their study:

“FRB 121102 is the only FRB for which a host galaxy and a distance were identified. It is also the only repeating FRB source from which we detected hundreds of FRBs by now. The radio spectrum of its FRBs is centered on a characteristic frequency and not covering a very broad band. This has important implications for the detectability of such FRBs, because in order to find them the radio observatory needs to be tuned to their frequency.”

Image of the sky where the radio burst FRB 121102 was found, in the constellation Auriga. You can see its location with a green circle. At left is supernova remnant S147 and at right, a star formation area called IC 410. Credit: Rogelio Bernal Andreo (DeepSkyColors.com)

Based on what is known about FRB 121102, Fialkov and Loeb conducted a series of calculations that assumed that it’s behavior was representative of all FRBs. They then projected how many FRBs would exist across the entire sky and determined that within the observable Universe, a FRB would likely be taking place once every second. As Dr. Fialkov explained:

“Assuming that FRBs are produced by galaxies of a particular type (e.g., similar to FRB 121102) we can calculate how many FRBs have to be produced by each galaxy to explain the existing observations (i.e., 2000 per sky per day). With this number in mind we can infer the production rate for the entire population of galaxies. This calculation shows that an FRB occurs every second when accounting for all the faint events.”

While the exact nature and origins of FRBs are still unknown – suggestions include rotating neutron stars and even alien intelligence! – Fialkov and Loeb indicate that they could be used to study the structure and evolution of the Universe. If indeed they occur with such regular frequency throughout the cosmos, then more distant sources could act as probes which astronomers would then rely on to plumb the depths of space.

For instance, over vast cosmic distances, there is a significant amount of intervening material that makes it difficult for astronomers to study the Cosmic Microwave Background (CMB) – the leftover radiation from the Big Bang. Studies of this intervening material could lead to a new estimates of just how dense space is – i.e. how much of it is composed of ordinary matter, dark matter, and dark energy – and how rapidly it is expanding.

Gemini composite image of the field around FRB 121102, the only repeating FRB discovered so far. Credit: Gemini Observatory/AURA/NSF/NRC

And as Prof. Loeb indicated, FRBs could also be used to explore enduring cosmlogical questions, like how the “Dark Age” of the Universe ended:

“FRBs can be used to measure the column of free electrons towards their source. This can be used to measure the density of ordinary matter between galaxies in the present-day universe. In addition, FRBs at early cosmic times can be used to find out when the ultraviolet light from the first stars broke up the primordial atoms of hydrogen left over from the Big Bang into their constituent electrons and protons.”

The “Dark Age”, which occurred between 380,000 and 150 million years after the Big Bang, was characterized by a “fog” of hydrogen atoms interacting with photons. As a result of this, the radiation of this period is undetectable by our current instruments. At present, scientists are still attempting to resolve how the Universe made the transition between these “Dark Ages” and subsequent epochs when the Universe was filled with light.

This period of “reionization”, which took place 150 million to 1 billion years after the Big Bang, was when the first stars and quasars formed. It is generally believed that UV light from the first stars in the Universe traveled outwards to ionize the hydrogen gas (thus clearing the fog). A recent study also suggested that black holes that existed in the early Universe created the necessary “winds” that allowed this ionizing radiation to escape.

To this end, FRBs could be used to probe into this early period of the Universe and determine what broke down this “fog” and allowed light to escape. Studying very distant FRBs could allow scientists to study where, when and how this process of “reionization” occurred. Looking ahead, Fialkov and Loeb explained how future radio telescopes will be able to discover many FRBs.

The planned Square Kilometer Array will be the world’s largest radio telescope when it begins operations in 2018. Credit: SKA

“Future radio observatories, like the Square Kilometer Array, will be sensitive enough to detect FRBs from the first generation of galaxies at the edge of the observable universe,” said Prof. Loeb. “Our work provides the first estimate of the number and properties of the first flashes of radio waves that lit up in the infant universe.”

And then there’s the Canadian Hydrogen Intensity Mapping Experiment (CHIME) at the at the Dominion Radio Astrophysical Observatory in British Columbia, which recently began operating. These and other instruments will serve as powerful tools for detecting FRBs, which in turn could be used to view previously unseen regions of time and space, and unlock some of the deepest cosmological mysteries.

“[W]e find that a next generation telescope (with a much better sensitivity than the existing ones) is expected to see many more FRBs than what is observed today,” said Dr. Fialkov. “This would allow to characterize the population of FRBs and identify their origin. Understanding the nature of FRBs will be a major breakthrough. Once the properties of these sources are known, FRBs can be used as cosmic beacons to explore the Universe. One application is to study the history of reionization (cosmic phase transition when the inter-galactic gas was ionized by stars).”

It is an inspired thought, using natural cosmic phenomena as research tools. In that respect, using FRBs to probe the most distant objects in space (and as far back in time as we can) is kind of like using quasars as navigational beacons. In the end, advancing our knowledge of the Universe allows us to explore more of it.

Further Reading: CfA, Astrophysical Journal Letters

NASA is Planning to Test Pulsars as Cosmic Navigation Beacons

When a large star undergoes gravitational collapse near the end of its lifespan, a neutron star is often the result. This is what remains after the outer layers of the star have been blown off in a massive explosion (i.e. a supernova) and the core has compressed to extreme density. Afterwards, the star’s rotation rate increases considerably, and where they emit beams of electromagnetic radiation, they become “pulsars”.

And now, 50 years after they were first discovered by British astrophysicist Jocelyn Bell, the first mission devoted to the study of these objects is about to be mounted. It is known as the Neutron Star Interior Composition Explorer (NICER), a two-part experiment that will be deployed to the International Space Station this summer. If all goes well, this platform will shed light on one of the greatest astronomical mysteries, and test out new technologies.

Astronomers have been studying neutron stars for almost a century, which have yielded some very precise measurements of their masses and radii. However, what actually transpires in the interior of a neutron star remains an enduring mystery. While numerous models have been advanced that describe the physics governing their interiors, it is still unclear how matter would behave under these types of conditions.

Not surprising, since neutron stars typically hold about 1.4 times the mass of our Sun (or 460,000 times the mass of the Earth) within a volume of space that is the size of a city. This kind of situation, where a considerable amount of matter is packed into a very small volume – resulting in crushing gravity and an incredible matter density – is not seen anywhere else in the Universe.

As Keith Gendreau, a scientist at NASA’s Goddard Space Flight Center, explained in a recent NASA press statement:

“The nature of matter under these conditions is a decades-old unsolved problem. Theory has advanced a host of models to describe the physics governing the interiors of neutron stars. With NICER, we can finally test these theories with precise observations.”

NICE was developed by NASA’s Goddard Space Flight Center with the assistance of the Massachusetts Institute of Technology (MIT), the Naval Research Laboratory, and universities across the U.S. and Canada. It consists of a refrigerator-sized apparatus that contains 56 X-ray telescopes and silicon detectors. Though it was originally intended to be deployed late in 2016, a launch window did not become available until this year.

Once installed as an external payload aboard the ISS, it will gather data on neutron stars (mainly pulsars) over an 18-month period by observing neutron stars in the X-ray band. Even though these stars emit radiation across the spectrum, X-ray observations are believed to be the most promising when it comes to revealing things about their structure and various high-energy phenomena associated with them.

SEXTANT will demonstrate a GPS-like absolute position determination capability by observing millisecond pulsars. Credit: NASA

These include starquakes, thermonuclear explosions, and the most powerful magnetic fields known in the Universe. To do this, NICER will collect X-rays generated from these stars’ magnetic fields and magnetic poles. This is key, since it is at the poles that the strength of a neutron star’s magnetic fields causes particles to be trapped and rain down on the surface, which produces X-rays.

In pulsars, it is these intense magnetic fields which cause energetic particles to become focused beams of radiation. These beams are what give pulsars their name, as they appear like flashes thanks to the star’s rotation (giving them their “lighthouse”-like appearance). As physicists have observed, these pulsations are predictable, and can therefore be used the same way atomic-clocks and Global Positioning System are here on Earth.

While the primary goal of NICER is science, it also offers the possibility of testing new forms of technology. For instance, the instrument will be used to conduct the first-ever demonstration of autonomous X-ray pulsar-based navigation. As part of the Station Explorer for X-ray Timing and Navigation Technology (SEXTANT), the team will use NICER’s telescopes to detect the X-ray beams generated by pulsars to estimate the arrival times of their pulses.

The team will then use specifically-designed algorithms to create an on-board navigation solution. In the future, interstellar spaceships could theoretically rely on this to calculate their location autonomously. This wold allow them to find their way in space without having to rely on NASA’s Deep Space Network (DSN), which is considered to be the most sensitive telecommunications system in the world.

Beyond navigation, the NICER project also hopes to conduct the first-ever test of the viability of X-ray based-communications (XCOM). By using X-rays to send and receive data (in the same way we currently use radio waves), spacecraft could transmit data at the rate of gigabits per second over interplanetary distances. Such a capacity could revolutionize the way we communicate with crewed missions, rover and orbiters.

Central to both demonstrations is the Modulated X-ray Source (MXS), which the NICER team developed to calibrate the payload’s detectors and test the navigation algorithms. Generating X-rays with rapidly varying intensity (by switching on and off many times per second), this device will simulate a neutron star’s pulsations. As Gendreau explained:

“This is a very interesting experiment that we’re doing on the space station. We’ve had a lot of great support from the science and space technology folks at NASA Headquarters. They have helped us advance the technologies that make NICER possible as well as those that NICER will demonstrate. The mission is blazing trails on several different levels.”

It is hoped that the MXS will be ready to ship to the station sometime next year; at which time, navigation and communication demonstrations could begin. And it is expected that before July 25th, which will mark the 50th anniversary of Bell’s discovery, the team will have collected enough data to present findings at scientific conferences scheduled for later this year.

If successful, NICER could revolutionize our understanding of how neutron stars (and how matter behaves in a super-dense state) behaves. This knowledge could also help us to understand other cosmological mysteries such as black holes. On top of that, X-ray communications and navigation could revolutionize space exploration and travel as we know it. In addition to providing greater returns from robotic missions located closer to home, it could also enable more lucrative missions to locations in the outer Solar System and even beyond.

Further Reading: NASA

Is the Universe Perfect for Life?

Doesn’t it feel like the Universe is perfectly tuned for life? Actually, it’s a horrible hostile place, delivering the bare minimum for human survival.

Consider that incomprehensible series of events that brought you to this moment. In a way that we still don’t understand, a complex mix of chemicals came together in just the right combination to kick off the evolution of life.

Generation after generation of bacteria, insects, fish, lizards, mammals and eventually humans somehow successfully found a buddy and passed along their genetic material to another generation. Clever humans invented computers, the internet, YouTube, and somehow you found your way to this exact video, to hear these words. Whoa.

It’s amazing to consider the Universe we live in, and how it’s perfectly tuned for life. If just a single variable was a little bit different, life as we know it probably wouldn’t exist. Gravity might be a repulsive force. Pokemons might catch you.

Doesn’t it feel like the Universe was created especially for us? I mean, didn’t I already tell you that we’re all the center of the Universe?

I’m sad to say, but this couldn’t be further from the truth. The reality is that the Universe is 100% completely inhospitable. Well, apart from a thin layer on the surface of our Earth, but that’s got to be a rounding error. A fraction of a fraction of a fraction of the teeniest percent of the volume of the Universe. The rest of the Universe is bunk.

If I was plucked out of our cozy environment and dropped into the near vacuum of pretty much anywhere else, the only resource would be a handful of hydrogen atoms. And what can you do with a few hydrogen atoms? Nothing. It might even give Bear Grylls a run for his money. He might have a little more trouble on a star’s surface, crisping up in a heartbeat.

Into a black hole? Surface of a neutron star? Near an exploding supernova? Please enjoy the crushing pressures and hellish temperatures of Venus, or the freezing irradiated surface of Mars.

Earth itself is mostly a deathtrap. Travel down a few kilometers and you’d bake and crush from the rising temperatures of the Earth’s interior. Travel up and the air gets thin, cold and killy. In fact, without our technology heating, cooling, or helping us breathe, we wouldn’t last more than a few days on most of the planet.

Panorama of one area of Mars, from Sol 173. Credit: NASA/JPL/Caltech/Malin Space Science Systems. Image editing by
Panorama of the part of Mars, from Sol 173. Credit: NASA/JPL/Caltech/Malin Space Science Systems. Image editing by

When you think about the landscape of time, we even live in a brief thumbnail of a moment when Earth is hospitable. Over the next few billion years, the Sun is going to heat up to the point that the surface of Earth will resemble the surface of Venus. And then the last hospitable hidey-hole in the entire Universe, that we know of, will wink out. The Universe is as inhospitable as it could possibly be. That is, without being completely inhospitable.

Especially when you consider the timeframes, and the long future when all the stars have died, where there’s nothing but black holes and frozen matter, and the Universe finally ditches that rounding error, and becomes 100% purely inhospitable.

Cosmologists use a term known as the anthropic principle to explain this very special moment we find ourselves in. There’s the greater anthropic principle that says the Universe wouldn’t be here without us to observe it, but that seems nutty and egotistical.

The lesser anthropic principle says that if the Universe turned out any differently, we wouldn’t be here to observe it.

First ever image of Earth Taken by Mars Color Camera aboard India’s Mars Orbiter Mission (MOM) spacecraft while orbiting Earth and before the Trans Mars Insertion firing on Dec. 1, 2013. Image is focused on the Indian subcontinent.  Credit: ISRO
First ever image of Earth Taken by Mars Color Camera aboard India’s Mars Orbiter Mission (MOM) spacecraft while orbiting Earth and before the Trans Mars Insertion firing on Dec. 1, 2013. Image is focused on the Indian subcontinent. Credit: ISRO

Imagine you threw a dart out the window of an airplane and it landed in a tiny spot on the surface of the Earth. What were the chances that it would land there? Almost zero. What a lucky spot.

You can imagine all kinds of other even more inhospitable Universes, where the conditions were never good enough for life to evolve, and so intelligent civilizations could never even ask the question, “Is Our Universe Perfect for Life.”

So when you look out across a meadow in the springtime. The birds are chirping, and there’s new growth everywhere, don’t forget about the boiling rock magma beneath your feet, the frigid air and then vacuum above your head, and the whole Universe of burning, radiating, impacting objects trying their best to kill you.

Of all the extreme environments in the Universe, which ones do you find most fascinating? Tell us in the comments below.

Gamma Ray Bursts Limit The Habitability of Certain Galaxies, Says Study

Gamma ray bursts (GRBs) are some of the brightest, most dramatic events in the Universe. These cosmic tempests are characterized by a spectacular explosion of photons with energies 1,000,000 times greater than the most energetic light our eyes can detect. Due to their explosive power, long-lasting GRBs are predicted to have catastrophic consequences for life on any nearby planet. But could this type of event occur in our own stellar neighborhood? In a new paper published in Physical Review Letters, two astrophysicists examine the probability of a deadly GRB occurring in galaxies like the Milky Way, potentially shedding light on the risk for organisms on Earth, both now and in our distant past and future.

There are two main kinds of GRBs: short, and long. Short GRBs last less than two seconds and are thought to result from the merger of two compact stars, such as neutron stars or black holes. Conversely, long GRBs last more than two seconds and seem to occur in conjunction with certain kinds of Type I supernovae, specifically those that result when a massive star throws off all of its hydrogen and helium during collapse.

Perhaps unsurprisingly, long GRBs are much more threatening to planetary systems than short GRBs. Since dangerous long GRBs appear to be relatively rare in large, metal-rich galaxies like our own, it has long been thought that planets in the Milky Way would be immune to their fallout. But take into account the inconceivably old age of the Universe, and “relatively rare” no longer seems to cut it.

In fact, according to the authors of the new paper, there is a 90% chance that a GRB powerful enough to destroy Earth’s ozone layer occurred in our stellar neighborhood some time in the last 5 billion years, and a 50% chance that such an event occurred within the last half billion years. These odds indicate a possible trigger for the second worst mass extinction in Earth’s history: the Ordovician Extinction. This great decimation occurred 440-450 million years ago and led to the death of more than 80% of all species.

Today, however, Earth appears to be relatively safe. Galaxies that produce GRBs at a far higher rate than our own, such as the Large Magellanic Cloud, are currently too far from Earth to be any cause for alarm. Additionally, our Solar System’s home address in the sleepy outskirts of the Milky Way places us far away from our own galaxy’s more active, star-forming regions, areas that would be more likely to produce GRBs. Interestingly, the fact that such quiet outer regions exist within spiral galaxies like our own is entirely due to the precise value of the cosmological constant – the factor that describes our Universe’s expansion rate – that we observe. If the Universe had expanded any faster, such galaxies would not exist; any slower, and spirals would be far more compact and thus, far more energetically active.

In a future paper, the authors promise to look into the role long GRBs may play in Fermi’s paradox, the open question of why advanced lifeforms appear to be so rare in our Universe. A preprint of their current work can be accessed on the ArXiv.

How CERN’s Discovery of Exotic Particles May Affect Astrophysics

You may have heard that CERN announced the discovery (confirmation, actually. See addendum below.) of a strange particle known as Z(4430).  A paper summarizing the results has been published on the physics arxiv, which is a repository for preprint (not yet peer reviewed) physics papers.  The new particle is about 4 times more massive than a proton, has a negative charge, and appears to be a theoretical particle known as a tetraquark.  The results are still young, but if this discovery holds up it could have implications for our understanding of neutron stars.

A periodic table of elementary particles. Credit: Wikipedia
A periodic table of elementary particles.
Credit: Wikipedia

The building blocks of matter are made of leptons (such as the electron and neutrinos) and quarks (which make up protons, neutrons, and other particles).  Quarks are very different from other particles in that they have an electric charge that is 1/3 or 2/3 that of the electron and proton.  They also possess a different kind of “charge” known as color.  Just as electric charges interact through an electromagnetic force, color charges interact through the strong nuclear force.  It is the color charge of quarks that works to hold the nuclei of atoms together. Color charge is much more complex than electric charge.  With electric charge there is simply positive (+) and its opposite, negative (-).  With color, there are three types (red, green, and blue) and their opposites (anti-red, anti-green, and anti-blue).

Because of the way the strong force works, we can never observe a free quark.  The strong force requires that quarks always group together to form a particle that is color neutral. For example, a proton consists of three quarks (two up and one down), where each quark is a different color.  With visible light, adding red, green and blue light gives you white light, which is colorless. In the same way, combining a red, green and blue quark gives you a particle which is color neutral.  This similarity to the color properties of light is why quark charge is named after colors.

Combining a quark of each color into groups of three is one way to create a color neutral particle, and these are known as baryons.  Protons and neutrons are the most common baryons.  Another way to combine quarks is to pair a quark of a particular color with a quark of its anti-color.  For example, a green quark and an anti-green quark could combine to form a color neutral particle.  These two-quark particles are known as mesons, and were first discovered in 1947.  For example, the positively charged pion consists of an up quark and an antiparticle down quark.

Under the rules of the strong force, there are other ways quarks could combine to form a neutral particle.  One of these, the tetraquark, combines four quarks, where two particles have a particular color and the other two have the corresponding anti-colors.  Others, such as the pentaquark (3 colors + a color anti-color pair) and the hexaquark (3 colors + 3 anti-colors) have been proposed.  But so far all of these have been hypothetical.  While such particles would be color neutral, it is also possible that they aren’t stable and would simply decay into baryons and mesons.

There has been some experimental hints of tetraquarks, but this latest result is the strongest evidence of 4 quarks forming a color neutral particle.  This means that quarks can combine in much more complex ways than we originally expected, and this has implications for the internal structure of neutron stars.

Very simply, the traditional model of a neutron star is that it is made of neutrons.  Neutrons consist of three quarks (two down and one up), but it is generally thought that particle interactions within a neutron star are interactions between neutrons.  With the existence of tetraquarks, it is possible for neutrons within the core to interact strongly enough to create tetraquarks.  This could even lead to the production of pentaquarks and hexaquarks, or even that quarks could interact individually without being bound into color neutral particles.  This would produce a hypothetical object known as a quark star.

This is all hypothetical at this point, but verified evidence of tetraquarks will force astrophysicists to reexamine some the assumptions we have about the interiors of neutron stars.

Addendum: It has been pointed out that CERN’s results are not an original discovery, but rather a confirmation of earlier results by the Belle Collaboration.  The Belle results can be found in a 2008 paper in Physical Review Letters, as well as a 2013 paper in Physical Review D.  So credit where credit is due.

Home Computers Discover Gamma-Ray Pulsars

Imagine that you’re innocently running your computer in pursuit of helping data crunch a huge science project. Then, out of the thousands of machines running the project, yours happens to stumble across a discovery. That’s what happened to several volunteers with [email protected], which seeks pulsars in data from the Fermi Gamma-Ray Space Telescope, among other projects.

“At first I was a bit dumbfounded and thought someone was playing a hoax on me. But after I did some research,” everything checked out. That someone as insignificant as myself could make a difference was amazing,” stated Kentucky resident Thomas M. Jackson, who contributed to the project.

Pulsars, a type of neutron star, are the leftovers of stars that exploded as supernovae. They rotate rapidly, with such precision in their rotation periods that they have sometimes been likened to celestial clocks. Although the discovery is exciting to the eight volunteers because they are the first to find these gamma-ray pulsars as part of a volunteer computing project, the pulsars also have some interesting scientific features.

Artist's illustration of a neutron star, a tiny remnant that remains after its predecessor star explodes. Here, the 12-mile (20-kilometer) sphere is compared with the size of Hannover, Germany. Credit: NASA's Goddard Space Flight Center
Artist’s illustration of a neutron star, a tiny remnant that remains after its predecessor star explodes. Here, the 12-mile (20-kilometer) sphere is compared with the size of Hannover, Germany. Credit: NASA’s Goddard Space Flight Center

The four pulsars were discovered in the plane of the Milky Way in an area that radio telescopes had looked at previously, but weren’t able to find themselves. This means that the pulsars are likely only visible in gamma rays, at least from the vantage point of Earth; the objects emit their radiation in a narrow direction with radio, but a wider stripe with gamma rays. (After the discoveries, astronomers used the Max Planck Institute for Radio Astronomy’s 100-meter Effelsberg radio telescope and the Australian Parkes Observatory to peer at those spots in the sky, and still saw no radio signals.)

Two of the pulsars also “hiccup” or exhibit a pulsar glitch, when the rotation sped up and then fell back to the usual rotation period a few weeks later. Astronomers are still learning more about these glitches, but they do know that most of them happen in young pulsars. All four pulsars are likely between 30,000 and 60,000 years old.

Artist's conception of a gamma-ray pulsar. Gamma rays are shown in purple, and radio radiation in green. Credit: NASA/Fermi/Cruz de Wilde
Artist’s conception of a gamma-ray pulsar. Gamma rays are shown in purple, and radio radiation in green. Credit: NASA/Fermi/Cruz de Wilde

“The first-time discovery of gamma-ray pulsars by [email protected] is a milestone – not only for us but also for our project volunteers. It shows that everyone with a computer can contribute to cutting-edge science and make astronomical discoveries,” stated co-author Bruce Allen, principal investigator of [email protected] “I’m hoping that our enthusiasm will inspire more people to help us with making further discoveries.”

[email protected] is run jointly by the Center for Gravitation and Cosmology at the University of Wisconsin–Milwaukee and the Albert Einstein Institute in Hannover, Germany. It is funded by the National Science Foundation and the Max Planck Society. As for the volunteers, their names were mentioned in the scientific literature and they also received certificates of discovery for their work.

Source: Max Planck Institute for Gravitational Physics

What is a Pulsar?

They are what is known as the “lighthouses” of the universe – rotating neutron stars that emit a focused beam of electromagnetic radiation that is only visible if you’re standing in it’s path. Known as pulsars, these stellar relics get their name because of the way their emissions appear to be “pulsating” out into space.

Not only are these ancient stellar objects very fascinating and awesome to behold, they are very useful to astronomers as well. This is due to the fact that they have regular rotational periods, which produces a very precise internal in its pulses – ranging from milliseconds to seconds.

Description:

Pulsars are types of neutron stars; the dead relics of massive stars. What sets pulsars apart from regular neutron stars is that they’re highly magnetized, and rotating at enormous speeds. Astronomers detect them by the radio pulses they emit at regular intervals.

An artist’s impression of an accreting X-ray millisecond pulsar. The flowing material from the companion star forms a disk around the neutron star which is truncated at the edge of the pulsar magnetosphere. Credit: NASA / Goddard Space Flight Center / Dana Berry

Formation:

The formation of a pulsar is very similar to the creation of a neutron star. When a massive star with 4 to 8 times the mass of our Sun dies, it detonates as a supernova. The outer layers are blasted off into space, and the inner core contracts down with its gravity. The gravitational pressure is so strong that it overcomes the bonds that keep atoms apart.

Electrons and protons are crushed together by gravity to form neutrons. The gravity on the surface of a neutron star is about 2 x 1011 the force of gravity on Earth. So, the most massive stars detonate as supernovae, and can explode or collapse into black holes. If they’re less massive, like our Sun, they blast away their outer layers and then slowly cool down as white dwarfs.

But for stars between 1.4 and 3.2 times the mass of the Sun, they may still become supernovae, but they just don’t have enough mass to make a black hole. These medium mass objects end their lives as neutron stars, and some of these can become pulsars or magnetars. When these stars collapse, they maintain their angular momentum.

But with a much smaller size, their rotational speed increases dramatically, spinning many times a second. This relatively tiny, super dense object, emits a powerful blast of radiation along its magnetic field lines, although this beam of radiation doesn’t necessarily line up with it’s axis of rotation. So, pulsars are simply rotating neutron stars.

And so, from here on Earth, when astronomers detect an intense beam of radio emissions several times a second, as it rotates around like a lighthouse beam – this is a pulsar.

History:

The first pulsar was discovered in 1967 by Jocelyn Bell Burnell and Antony Hewis, and it surprised the scientific community by the regular radio emissions it transmitted. They detected a mysterious radio emission coming from a fixed point in the sky that peaked every 1.33 seconds. These emissions were so regular that some astronomers thought it might be evidence of communications from an intelligent civilization.

Although Burnell and Hewis were certain it had a natural origin, they named it LGM-1, which stands for “little green men”, and subsequent discoveries have helped astronomers discover the true nature of these strange objects.

Astronomers theorized that they were rapidly rotating neutron stars, and this was further supported by the discovery of a pulsar with a very short period (33-millisecond) in the Crab nebula. There have been a total of 1600 found so far, and the fastest discovered emits 716 pulses a second.

Later on, pulsars were found in binary systems, which helped to confirm Einstein’s theory of general relativity. And in 1982, a pulsar was found with a rotation period of just 1.6 microseconds. In fact, the first extrasolar planets ever discovered were found orbiting a pulsar – of course, it wouldn’t be a very habitable place.

Interesting Facts:

When a pulsar first forms, it has the most energy and fastest rotational speed. As it releases electromagnetic power through its beams, it gradually slows down. Within 10 to 100 million years, it slows to the point that its beams shut off and the pulsar becomes quiet.

When they are active, they spin with such uncanny regularity that they’re used as timers by astronomers. In fact, it is said that certain types of pulsars rival atomic clocks in their accuracy in keeping time.

Pulsars also help us search for gravitational waves, probe the interstellar medium, and even find extrasolar planets in orbit. In fact, the first extrasolar planets were discovered around a pulsar in 1992, when astronomers Aleksander Wolszczan and Dale Frail announced the discovery of a multi-planet planetary system around PSR B1257+12 – a millisecond pulsar now known to have two extrasolar planets.

Artist's impression of the planets orbiting PSR B1257+12. Credit: NASA/JPL-Caltech/R. Hurt (SSC)
Artist’s impression of the planets orbiting PSR B1257+12. Credit: NASA/JPL-Caltech/R. Hurt (SSC)

It has even been proposed that spacecraft could use them as beacons to help navigate around the Solar System. On NASA’s Voyager spacecraft, there are maps that show the direction of the Sun to 14 pulsars in our region. If aliens wanted to find our home planet, they couldn’t ask for a more accurate map.

We have written many articles about stars here on Universe Today. Here’s an article about a newly discovered gamma ray pulsar, and here’s an article about how millisecond pulsars spin so fast.

If you’d like more information on stars, check out Hubblesite’s News Releases about Stars, and here’s the stars and galaxies homepage.

We have recorded several episodes of Astronomy Cast about stars. Here are two that you might find helpful: Episode 12: Where Do Baby Stars Come From, and Episode 13: Where Do Stars Go When they Die?

Newly Discovered Fast Radio Bursts May be Colliding Neutron Stars

The Universe is sizzling with undiscovered phenomena. Only last month astronomers heard four unexpected bumps in the night. These Fast Radio Bursts released torrents of energy, each occurred only once, and lasted a few thousandths of a second. Their origin has since mystified astronomers.

Dismissing my first guess, which includes a feverish Jodie Foster verifying the existence of extraterrestrial life, astronomers have found a more likely answer. Two neutron stars collide, but before doing so produce a quick burst of radio emission, which we later observe as a Fast Radio Burst.

Our first hint? These Fast Radio Bursts are extra-galactic in origin.  The exact distance is quantifiable from a “dispersion measure – the frequency dependent time delay of the radio signal,” Dr. Tomonori Totani, lead author on the paper, told Universe Today. “This is proportional to the number of electrons along the line of sight.”

For all bursts, the short-wavelength component arrived at the telescope a fraction of a second before the longer wavelengths.  This is due to an effect known as interstellar dispersion: through any medium, longer-wavelength light moves slightly slower than short-wavelength light.

Light from extra-galactic objects will have to travel through intergalactic space, which is teeming with electrons in clouds of cold plasma. The farther the light travels, the more electrons it will have to travel through, and the greater the time delay between arriving wavelength components. By the time light reaches the Earth, it has been dispersed, and the amount of dispersion is directly correlated with distance.

These Fast Radio Bursts are likely to have originated anywhere from 5 to 10 billion light years away.

While the exact source of these Fast Radio Bursts has been highly debated, a recent hypothesis concludes that they are the result of merging neutron stars in the distant Universe.

In the final milliseconds before merging, the rotation periods of the two neutron stars synchronize – they become tidally locked to one another as the Moon is tidally locked to the Earth. At this point their magnetic fields also synchronize. Energetic charged particles spiral along the strong magnetic field lines and emit a beam of radio synchrotron emission.

Known neutron star magnetic field strengths are consistent with the radio flux observed in these Fast Radio Bursts.  The emission then ceases in a few milliseconds when the two neutron stars have collided, which explains the short duration of these Fast Radio Bursts.

Not only does this mechanism describe both the high energy and the time duration of these bursts, but they’re inferred occurrence rate as well. It’s likely that 100,000 Fast Radio Bursts occur each day. This matches the likely neutron star merger rate.

Merging neutrons stars will also create gravitational waves – ripples in the curvature of spacetime that propagate away from the event. Dr. Totani emphasized that the next step will be to perform a correlated search of gravitational waves and Fast Radio Bursts. Such a fast rate estimate is certainly good news for scientists hoping to detect gravitational waves in the nearby future.

The Universe is bursting with energy – literally – every 10 seconds, and until recently we simply had no idea. This recently discovered phenomenon is likely to be the center of a new active area of research. And I have no doubt that it will lead to exciting discoveries that just may break trends and burst into new territories.

The discovery paper may be found here, while the paper analyzing neutron stars as a likely source may be found here.

Earth’s Gold Came From Colliding Stars

Are you wearing a gold ring? Or perhaps gold-plated earrings? Maybe you have some gold fillings in your teeth… for that matter, the human body itself naturally contains gold — 0.000014%, to be exact! But regardless of where and how much of the precious yellow metal you may have with you at this very moment, it all ultimately came from the same place.

And no, I don’t mean Fort Knox, the jewelry store, or even under the ground — all the gold on Earth likely originated from violent collisions between neutron stars, billions of years in the past.

Recent research by scientists at the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Massachusetts has revealed that considerable amounts of gold — along with other heavy elements — are produced during impacts between neutron stars, the super-dense remains of stars originally 1.4 to 9 times the mass of our Sun.

The team’s investigation of a short-duration gamma-ray outburst that occurred in June (GRB 130603B) showed a surprising residual near-infrared glow, possibly from a cloud of material created during the stellar merger. This cloud is thought to contain a considerable amount of freshly-minted heavy elements, including gold.

“We estimate that the amount of gold produced and ejected during the merger of the two neutron stars may be as large as 10 moon masses – quite a lot of bling!” said lead author Edo Berger.

"With this remnant of a dead neutron star, I thee wed." (FreeDigitalPhotos.net/bigjom)
“With this remnant of a dead neutron star, I thee wed.” (FreeDigitalPhotos.net/bigjom)

The mass of the Moon is 7.347 x 1022 kg… about 1.2% the mass of Earth. The collision between these neutron stars then, 3.9 billion light-years away, produced 10 times that much gold based on the team’s estimates.

Quite a lot of bling, indeed.

Gamma-ray bursts come in two varieties – long and short – depending on the duration of the gamma-ray flash. GRB 130603B, detected by NASA’s Swift satellite on June 3rd, lasted for less than two-tenths of a second.

Although the gamma rays disappeared quickly, GRB 130603B also displayed a slowly fading glow dominated by infrared light. Its brightness and behavior didn’t match the typical “afterglow” created when a high-speed jet of particles slams into the surrounding environment.

Instead, the glow behaved like it came from exotic radioactive elements. The neutron-rich material ejected by colliding neutron stars can generate such elements, which then undergo radioactive decay, emitting a glow that’s dominated by infrared light – exactly what the team observed.

“We’ve been looking for a ‘smoking gun’ to link a short gamma-ray burst with a neutron star collision,” said Wen-fai Fong, a graduate student at CfA and a co-author of the paper. “The radioactive glow from GRB 130603B may be that smoking gun.”

The team calculates that about one-hundredth of a solar mass of material was ejected by the gamma-ray burst, some of which was gold. By combining the estimated gold produced by a single short GRB with the number of such explosions that have likely occurred over the entire age of the Universe, all the gold in the cosmos – and thus on Earth – may very well have come from such gamma-ray bursts.

Watch an animation of two colliding neutron stars along with the resulting GRB below (Credit: Dana Berry, SkyWorks Digital, Inc.):

How much gold is there on Earth, by the way? Since most of it lies deep inside Earth’s core and is thus unreachable, the total amount ever retrieved by humans over the course of history is surprisingly small: about 172,000 tonnes, or enough to make a cube 20.7 meters (68 feet) per side (based on the Thomson Reuters GFMS annual survey.) Some other estimates put this amount at slightly more or less, but the bottom line is that there really isn’t all that much gold available in Earth’s crust… which is partly what makes it (and other “precious” metals) so valuable.

And perhaps the knowledge that every single ounce of that gold was created by dead stars smashing together billions of years ago in some distant part of the Universe would add to that value.

“To paraphrase Carl Sagan, we are all star stuff, and our jewelry is colliding-star stuff,” Berger said.

The team’s findings were presented today in a press conference at the CfA in Cambridge. (See the paper here.)

Source: Harvard-Smithsonian CfA