‘Failed’ Star Rapidly Orbits ‘Dead’ Star in Weird Stellar Pairing


The galaxy may be filled with weird stellar wonders, but you’d be hard-pressed to find a binary system stranger than WD1202-024.

First thought to be an isolated white dwarf star approximately 40% the mass of our sun, astronomers studying observational data from NASA’s Kepler space telescope realized the stellar husk has company. In an extremely fast 71-minute orbit, the star has a brown dwarf, 67 times the mass of Jupiter, in tow — an unprecedented find.

White dwarfs are formed after sun-like stars run out of fuel and die. This will be the fate of our sun in about five billion years time, after it becomes depleted of hydrogen in its core and puffs-up into a red giant. Shedding its outer layers after a period of violent stellar turmoil, a planetary nebula will form with a tiny mass of degenerate matter — a white dwarf — in its center. Earth would be toast long before the sun turns into a red giant, however.

But in the case of WD1202-024, it seems that when it was a young star (before it passed through its final red giant phase), it had a brown dwarf in orbit.

Commonly known as “failed stars,” brown dwarfs are not massive enough to sustain sufficient fusion in their cores to spark the formation of a star. But they’re too massive to be called planets as they possess the internal circulation of material that is more familiar to stars (so with that in mind, I like to refer to brown dwarfs as “overachieving planets”). They are the bridge between stars and planets and fascinating objects in their own right.

But the brown dwarf in the WD1202 binary couldn’t have formed with only a 71-minute orbit around the white dwarf; it would have evolved further away. So what happened? After carrying out computer simulations of the system, the international team of researchers found a possible answer.

“It is similar to an egg-beater effect,” said astronomer Lorne Nelson, of Bishop’s University, Canada, during the American Astronomical Society meeting in Austin, Texas on June 6th. “The brown dwarf spirals in towards the center of the red giant and causes most of the mass of the red giant to be lifted off of the core and to be expelled. The result is a brown dwarf in an extraordinarily tight, short-period orbit with the hot helium core of the giant. That core then cools and becomes the white dwarf that we observe today.”

In the future, the researchers hypothesize, the brown dwarf will continue to orbit the white dwarf until energy is depleted from the system via gravitational waves. In less than 250 million years, the orbital distance will be so small that the extreme tidal forces exerted by the white dwarf will start to drag brown dwarf material into the star, cannibalizing it.

This will turn WD1202 into a cataclysmic variable (CV), causing its brightness to flicker as the brown dwarf material is extruded into an accretion disk orbiting the white dwarf.

What a way to go.


NASA Uses Gravitational Wave Detector Prototype to Detect ‘Space Mosquito’ Splats

Artist impression of ESA LISA Pathfinder in interplanetary space (ESA)

Imagine speeding down the highway and plowing into an unfortunate swarm of mosquitoes. Now imagine that you had the ability to precisely measure the mass of each mosquito, the speed at which it was traveling and the direction it was going before it exploded over your windscreen.

Granted, the technology to accomplish that probably isn’t feasible in such an uncontrolled environment. Factors such as vibration from the car’s motor and tires on the road, plus wind and air turbulence will completely drown out any “splat” from a minuscule insect’s body, rendering any signal difficult to decipher from noise.

But move your hypothetical “car and mosquitoes” into space — as silly as that may sound — and things become a lot less noisy. And now NASA is measuring its own special kind of “mosquito splat” signal by using a rather unlikely space experiment.

The European LISA Pathfinder spacecraft is a proof of concept mission that’s currently in space, orbiting a region of gravitational stability between the Earth and the sun — called the L1 point located a million miles away. The spacecraft was launched there in late 2015 to carry out precision tests of instruments that will eventually be used in the space-based gravitational wave detector eLISA. Inside the payload is a miniaturized laser interferometer system that measures the distance between two test masses.

When launched in 2034, eLISA (which stands for Evolved Laser Interferometer Space Antenna) will see three spacecraft, orbiting the sun at the L1 point, firing ultra-precise lasers at one another as part of a space-based gravitational wave detector. Now we actually know gravitational waves exist — after the US-based Laser Interferometer Gravitational-wave Observatory (or LIGO) detected the space-time ripples created after the collisions of black holes — excitement is building that we might, one day, be able to measure other phenomena, such as the ultra-low frequency gravitational waves that were created during the Big Bang.

But the only way we can do this is to send stunningly precise interferometers into space, away from our vibration-filled atmosphere to stand a chance of detecting some of the faintest space-time rumbles in our cosmos that would otherwise be drowned out by a passing delivery truck or windy day. And LISA Pathfinder is currently out there, testing a tiny laser interferometer in a near-perfect gravitational free-fall, making the slightest of slight adjustments with its “ultra-precise micro-propulsion system.”

Although LISA Pathfinder is a test (albeit a history-making test of incredible engineering ingenuity), NASA thinks that it could actually be used as an observatory in its own right; not for hunting gravitational waves, but for detecting comet dust.

Like our mosquito-windscreen analogy, spacecraft get hit by tiny particles all the time, and LISA Pathfinder is no exception. These micrometeoroides come from eons of evaporating comets and colliding asteroids. Although measuring less than the size of a grain of sand, these tiny particles zip around interplanetary space at astonishing speeds — well over 22,000 miles per hour (that’s 22 times faster than a hyper-velocity rifle round) — and can damage spacecraft over time, slowly eroding unprotected hardware.

Therefore, it would be nice if we could create a map of regions in the solar system that contain lots of these particles so we can be better prepared to face the risk. Although models of solar system evolution help and we can estimate the distribution of these particles, they’ve only ever been measured near Earth, so it would be advantageous to find the “ground truth” and measure them directly from another, unexplored region of the solar system.

This is where LISA Pathfinder comes in.

As the spacecraft gets hit by these minuscule particles, although they are tiny, their high speed ensures they pack a measurable punch. As scientists want the test weights inside the spacecraft to be completely shielded from any external force — whether that’s radiation pressure from the sun or marauding micro-space rocks — the spacecraft has been engineered to be an ultra-precise container that carefully adjusts its orientation an exact amount to directly counter these external forces (hence the “ultra-precise micro-propulsion system”).

When LISA Pathfinder is struck by space dust, it compensates with its ultra-precise micro-thrusters (ESA/NASA)

This bit is pretty awesome: Whenever these tiny space particles hit the spacecraft, it compensates for the impact and that compensation is registered as a “blip” in the telemetry being beamed back to Earth. After careful analysis of the various data streams, researchers are learning a surprising amount of information about these micrometeoroides — such as their mass, speed, direction of travel and even their possible origin! — all for the ultimate goal of getting to know the tiny pieces of junk that whiz around space.

“Every time microscopic dust strikes LISA Pathfinder, its thrusters null out the small amount of momentum transferred to the spacecraft,” said Diego Janches, of NASA’s Goddard Space Flight Center in Greenbelt, Md. “We can turn that around and use the thruster firings to learn more about the impacting particles. One team’s noise becomes another team’s data.”

So, it turns out that you can precisely measure a mosquito impact on your car’s windshield — so long as that “mosquito” is a particle of space dust and your “car” is a spacecraft a million miles from Earth.

NASA put together a great video, watch it:

Aside: So it turned out that I inadvertently tested the “car-mosquito” hypothesis when driving home from Las Vegas — though some of these were a lot bigger than mosquitoes…

This Black Hole Keeps Its Own White Dwarf ‘Pet’

The most compact star-black hole binary has been discovered, but the star seems to be perfectly happy whirling around the massive singularity twice an hour.

Credits: X-ray: NASA/CXC/University of Alberta/A.Bahramian et al.; Illustration: NASA/CXC/M.Weiss

A star in the globular cluster of 47 Tucanae is living on the edge of oblivion.

Located near a stellar-mass black hole at only 2.5 times the Earth-moon distance, the white dwarf appears to be in a stable orbit, but it’s still paying the price for being so intimate with its gravitational master. As observed by NASA’s Chandra X-ray Observatory and NuSTAR space telescope, plus the Australia Telescope Compact Array, gas is being pulled from the white dwarf, which then spirals into the black hole’s super-heated accretion disk.

47 Tucanae is located in our galaxy, around 14,800 light-years from Earth.

Eventually, the white dwarf will become so depleted of plasma that it will turn into some kind of exotic planetary-mass body or it will simply evaporate away. But one thing does appear certain, the white dwarf will remain in orbit and isn’t likely to get swallowed by the black hole whole any time soon.

“This white dwarf is so close to the black hole that material is being pulled away from the star and dumped onto a disk of matter around the black hole before falling in,” said Arash Bahramian, of the University of Alberta (Canada) and Michigan State University. “Luckily for this star, we don’t think it will follow this path into oblivion, but instead will stay in orbit.” Bahramian is the lead author of the study to be published in the journal Monthly Notices of the Royal Astronomical Society.

It was long thought that globular clusters were bad locations to find black holes, but the 2015 discovery of the binary system — called “X9” — generating quantities of radio waves inside 47 Tucanae piqued astronomers’ interest. Follow-up studies revealed fluctuating X-ray emissions with a period of around 28 minutes — the approximate orbital period of the white dwarf around the black hole.

So, how did the white dwarf become the pet of this black hole?

The leading theory is that the black hole collided with an old red giant star. In this scenario, the black hole would have quickly ripped away the bloated star’s outer layers, leaving a tiny stellar remnant — a white dwarf — in its wake. The white dwarf then became the black hole’s gravitational captive, forever trapped in its gravitational grasp. Its orbit would have become more and more compact as the system generated gravitational waves (i.e. ripples in space-time), radiating orbital energy away, shrinking its orbital distance to the configuration that it is in today.

It is now hoped that more binary systems of this kind will be found, perhaps revealing that globular clusters are in fact very good places to find black holes enslaving other stars.

Holographic Universe: Fermilab to Probe Smallest Space-Time Scales

Conceptual design of the Fermilab holometer (Fermilab)
Conceptual design of the Fermilab holometer (Fermilab)

During the hunt for the predicted ripples in space-time — known as gravitational waves — physicists stumbled across a rather puzzling phenomenon. Last year, I reported about the findings of scientists using the GEO600 experiment in Germany. Although the hi-tech piece of kit hadn’t turned up evidence for the gravitational waves it was seeking, it did turn up a lot of noise.

Before we can understand what this “noise” is, we need to understand how equipment designed to look for the space-time ripples caused by collisions between black holes and supernova explosions.

Gravitational wave detectors are incredibly sensitive to the tiniest change in distance. For example, the GEO600 experiment can detect a fluctuation of an atomic radius over a distance from the Earth to the Sun. This is achieved by firing a laser down a 600 meter long tube where it is split, reflected and directed into an interferometer. The interferometer can detect the tiny phase shifts in the two beams of light predicted to occur should a gravitational wave pass through our local volume of space. This wave is theorized to slightly change the distance between physical objects. Should GEO600 detect a phase change, it could be indicative of a slight change in distance, thus the passage of a gravitational wave.

While looking out for a gravitational wave signal, scientists at GEO600 noticed something bizarre. There was inexplicable static in the results they were gathering. After canceling out all artificial sources of the noise, they called in the help of Fermilab’s Craig Hogan to see if his expertise of the quantum world help shed light on this anomalous noise. His response was as baffling as it was mind-blowing. “It looks like GEO600 is being buffeted by the microscopic quantum convulsions of space-time,” Hogan said.

Come again?

The signal being detected by GEO600 isn’t a noise source that’s been overlooked, Hogan believes GEO600 is seeing quantum fluctuations in the fabric of space-time itself. This is where things start to get a little freaky.

According to Einstein’s view on the universe, space-time should be smooth and continuous. However, this view may need to be modified as space-time may be composed of quantum “points” if Hogan’s theory is correct. At its finest scale, we should be able to probe down the “Planck length” which measures 10-35 meters. But the GEO600 experiment detected noise at scales of less than 10-15 meters.

As it turns out, Hogan thinks that noise at these scales are caused by a holographic projection from the horizon of our universe. A good analogy is to think about how an image becomes more and more blurry or pixelated the more you zoom in on it. The projection starts off at Planck scale lengths at the Universe’s event horizon, but its projection becomes blurry in our local space-time. This hypothesis comes out of black hole research where the information that falls into a black hole is “encoded” in the black hole’s event horizon. For the holographic universe to hold true, information must be encoded in the outermost reaches of the Universe and it is projected into our 3 dimensional world.

But how can this hypothesis be tested? We need to boost the resolution of a gravitational wave detector-type of kit. Enter the “Holometer.”

Currently under construction in Fermilab, the Holometer (meaning holographic interferometer) will delve deep into this quantum realm at smaller scales than the GEO600 experiment. If Hogan’s idea is correct, the Holometer should detect this quantum noise in the fabric of space-time, throwing our whole perception of the Universe into a spin.

For more on this intriguing experiment, read the Symmety Magazine article “Hogan’s holometer: Testing the hypothesis of a holographic universe.”

Detecting Gravitational Waves on the Cheap

Forget building gravitational wave detectors costing hundreds of millions of dollars (I’m looking at you, LIGO), make use of the most accurate cosmic timekeepers instead and save a bundle.

The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) is a proposal that involves closely monitoring the regular flashes of spinning neutron stars (or pulsars) to detect very slight “shimmers” in their signal. Although the physics is crazy-complex, by tracking these shimmers over a suitably distributed number of pulsars could reveal the passage of gravitational waves.

However, there’s a problem with this plan; pulsars are notoriously tricky stellar objects, as my colleague Jennifer Ouellette points out:

The problem is that you need to closely monitor rapidly-spinning millisecond pulsars, which are (a) tough to find (only 150 have been found over nearly three decades since pulsars were first discovered), and (b) not very plentiful in the part of the night sky of interest to scientists (northern hemisphere). They tend to clump together in globular star clusters, which makes them useless for detecting gravitational waves.

However, according to results announced by the National Radio Astronomy Observatory (NRAO) at this week’s American Astronomical Society (AAS) meeting in Washington D.C., they’ve discovered 17 new pulsars with the help of NASA’s Fermi Gamma-Ray Space Telescope.

In addition to recent Fermi telescope pulsar discoveries, it would appear that the number of potential targets for NANOGrav are increasing, making a stronger case for the 10 year, $65 million project…

You have to wonder whether building the Laser Interferometer Gravitational-Wave Observatory (LIGO) was worth it (but you can’t be too careful, some terrorist organizations might want to use gravitational waves for evil, so it would be good if we detected them first).

Source: Discovery News

The Naked Singularity Recipe: Spin a Black Hole, Add Mass


The event horizon of a black hole is the point of no return. If anything, even light, strays within the bounds of this gravitational trap, it will never escape. The event horizon is what makes a black hole black.

But say if there was a way to remove the event horizon, leaving just the black hole’s singularity to be “seen” by the rest of the universe? What if there is a special condition that would allow this infinitely small, yet massive point to become naked?

Generally physicists agree that this is a physical impossibility, but the mathematics says otherwise; a naked singularity could be possible.

Previously on Astroengine, one “special condition” was investigated when an extreme black hole collision was simulated by a Caltech researcher. In this case, the black hole pair was smashed together, head-on, at a velocity close to the speed of light. The gravitational waves travelling away from the collision were then modelled and characterized. It turns out that after this insanely energetic impact, 14% of the total mass was converted into gravitational wave energy and both black holes merged as one.

While this might not be very realistic, it proved to be a very useful diagnostic tool to understand the conditions after the collision of two black holes. As an interesting observation, the Caltech researchers found that although the collision was extreme, and there was a huge amount of mass-energy conversion going on (plus, I’d imagine, a rather big explosion), neither black hole lost their event horizons.

Case closed, wouldn’t you think?

Actually, another theory as to how a black hole could be stripped naked has been knocking around for some time; what if you added mass to a black hole spinning at its maximum possible rate? Could the black hole be disrupted enough to shed its event horizon?

It turns out there’s a natural braking system that prevents this from happening. As soon as mass is dropped into the black hole, it is flung out of the event horizon by the black hole’s huge centrifugal force, preventing it from coming close to the singularity.

However, Ted Jacobson and Thomas Sotiriou at the University of Maryland at College Park have now improved upon this idea, sending mass in the same direction as the spinning black hole. Only this time, the black hole isn’t spinning at its fastest possible rate, the simulation lets the orbiting matter fall into the event horizon, speeding up its spin. The result? It appears to disrupt the black hole enough to strip away the event horizon, exposing the singularity.

The most interesting thing to come of this research is that swirling matter is falling into black holes all over the universe, speeding up their spin. Jacobson and Sotiriou may have stumbled on a viable mechanism that actually allows naked singularities in the cosmos. Unless nature has found another way to prevent the cosmic censorship hypothesis from being violated that is…

Source: New Scientist

Did Gravitational Waves Ring a Bell in 1987?

Gravitational waves generated by a binary system (MIT)
Gravitational waves generated by a binary system (MIT)

The hunt for gravitational waves continue, but unfortunately all gravitational wave hunters around the world are churning up nothing. Just noise. Could it be that this consequence of Einstein’s theory of General Relativity is horribly flawed? Probably not. Still, the search for these elusive waves has foxed physicists for many years. It has even come to the point that the laser interferometers used in an attempt to detect the tiny (and I mean TINY) changes in distances (as when the gravitational wave passes through us, space-time experiences a minuscule compression or expansion) have become so precise, the director of Fermilab thinks a German-UK gravitational wave detector is starting to detect the quanta of space-time itself.

However, do you ever get the feeling that we might be trying too hard? What if gravitational waves have already been detected? Say if these notoriously difficult ripples in space-time were detected over 20 years ago without using a laser interferometer? It turns out that an overlooked scientist may have found the answer to the gravitational wave problem by using nothing more than some aluminium bars and a well-timed supernova…
Continue reading “Did Gravitational Waves Ring a Bell in 1987?”

Gravitational Waves and Gravity Waves, What’s the Difference?


I’ve received this question so many times, so I thought I’d post, for reference purposes, the difference between a gravitational wave and a gravity wave. Yes, they are different creatures (although many authors would have you believe otherwise).

Gravitational waves are theoretical perturbations (ripples) in space-time. Much work is going into the discovery of gravitational waves using gravitational wave detectors like the US Laser Interferometer Gravitational-Wave Observatory (LIGO) or German-British GEO600, but so far, they have proven to be very elusive. In a previous Astroengine post, there is a new theory that perhaps gravitational wave detectors have reached a limit on their precision (i.e. the quanta of space-time, leading to the holographic universe conjecture). Gravitational waves, as predicted by Einstein’s theory of general relativity, are thought to exist, but have yet to be detected. There are indirect observations of gravitational waves, from observations of the slowing period of binary stars; energy is most likely being lost through gravitational wave generation. Gravitational waves are thought to be generated also by black hole collision, pulsars and supernovae. More on Gravitational Waves…

Gravity waves are physical perturbations driven by the restoring force of gravity in a terrestrial environment. A common example of this are waves formed at an air-water boundary (i.e. the surface of the ocean). Wind creates an instability in the ocean, the restoring gravity force pulls down on the water, while the buoyancy of the water pushes it back up. A perturbation then propagates (i.e. ocean waves). Extreme examples include tsunamis and tides. Perturbations in the atmosphere can also be caused by gravity, where rising/falling air tries to regain equilibrium (after being forced over a maintain range, say), but gravity and buoyancy forces will cause it to propagate as a wave. More on Gravity Waves…

So, gravitational waves are perturbations in space-time (over universal scales). Gravity waves are perturbations in atmospheres (planetary scale). They most certainly are not the same thing.

Is the Universe a Holographic Projection?

Luke and Obi-Wan look at a 3D hologram of Leia projected by R2D2 (Star Wars)
Luke and Obi-Wan look at a 3D hologram of Leia projected by R2D2 (Star Wars)

Could our cosmos be a projection from the edge of the observable Universe?

Sounds like a silly question, but scientists are seriously taking on this idea. As it happens, a gravitational wave detector in Germany is turning up null results on the gravitational wave detection front (no surprises there), but it may have discovered something even more fundamental than a ripple in space-time. The spurious noise being detected at the GEO600 experiment has foxed physicists for some time. However, a particle physicist from the accelerator facility Fermilab has stepped in with his suspicion that the GEO600 “noise” may not be just annoying static, it might be the quantum structure of space-time itself
Continue reading “Is the Universe a Holographic Projection?”

Can Gravitational Waves be Used for Evil?

Theoretical gravitational waves generated after a black hole collision. Can we surf them?
Theoretical gravitational waves generated after a black hole collision. Can we surf them?

Gravitational waves are a theoretical consequence of a propagating energy disturbance through space-time. They are predicted by Einstein’s general relativity equations, and astrophysicists are going to great pains to try to detect the faint signature from the passage of these waves through local space. Unfortunately, even though millions of dollars have been spent on international experiments, the gravitational wave remains in equation form; there is little (direct) evidence to support their existence.

However, this doesn’t stop the US military from worrying about them and commissioned a 40-page report into whether high frequency gravitational waves could be used by an enemy. Excuse me? Gravitational waves… as a weapon?
Continue reading “Can Gravitational Waves be Used for Evil?”