Artist’s impression of a massive asteroid belt in orbit around a star. Earth's water may not have all come from asteroids and comets, so maybe that's true for exoplanets. Credit: NASA-JPL / Caltech / T. Pyle (SSC)
What’s with all the metals in the atmosphere of white dwarfs, those things that are corpses of stars like our own Sun? While before scientists had theories about levitating star layers that “polluted” the white dwarfs, new research shows it’s more likely due to rocky material. More specifically, material left over from planet formation.
Researchers surveyed 89 of these objects with the Far Ultraviolet Spectroscopic Explorer, a NASA space telescope which operated from 1999 to 2008. The stars’ spectra was analyzed to see what distinctive wavelengths of elements showed up.
Scientists discovered that in one-third of these stars, the ratio of silicon to carbon material is pretty close to what is seen in rocks, and is much higher than what would be expected in stars. The work implies that only a fraction of stars like our Sun would have terrestrial planets, researchers added.
Artist’s impression of debris around a white dwarf star. Credit: NASA, ESA, STScI, and G. Bacon (STScI)
“The mystery of the composition of these stars is a problem we have been trying to solve for more than 20 years,” stated Martin Barstow of the University of Leicester, who led the research.
“It is exciting to realize that they are swallowing up the leftovers from planetary systems, perhaps like our own, with the prospect that more detailed follow-up work will be able to tell us about the composition of rocky planets orbiting other stars.”
You can read more about the research in the Monthly Notices of the Royal Astronomical Society. The research team includes Barstow’s daughter, Jo, who was doing a summer work placement in Leicester at the time. She is now working at Oxford University in the field of extrasolar planets.
It’s a staple of science fiction, restarting our dying star with some kind of atomic superbomb. Why is our Sun running out of fuel, and what can we actually do to get it restarted?
Stars die. Occasionally threatening the Earth and its civilization in a variety plot devices in science fiction. Fortunately there’s often a Bruce Willis coming in to save the day, delivering a contraption, possibly riding a giant bomb shaped like a spaceship, to the outer proximity of our dying Sun that magically fixes the broken star and all humanity is saved.
Is there any truth in this idea? If our Sun dies, can we just crack out a giant solar defibrillator and shock it back into life? Not exactly.
First, let’s review at how stars die. Our Sun is halfway through its life. It’s been going for about 4.5 billion years, and in 5 billion years it’ll use up all the hydrogen in its core, bloat up as a red giant, puff off its outer layers and collapse down into a white dwarf.
Is there a point in there, anywhere, that we could get it back to acting like a sun? Technically? Yes. Did you know it will only use up a fraction of its fuel during its lifetime? Only in the core of the Sun are the temperatures and pressures high enough for fusion reactions to take place. This region extends out to roughly 25% of the radius, which only makes up about 2% of the volume.
Outside the core is the radiative zone, where fusion doesn’t take place. Here, the only way gamma radiation can escape is to be absorbed and radiated countless times, until it reaches the next layer of the Sun: the convective zone. Here temperatures have dropped to the point that the whole region acts like a giant lava lamp. Huge blobs of superheated stellar plasma rise up within the star and release their energy into space. This radiative zone acts like a wall, keeping the potential fuel in the convective zone away from the fusion furnace.
Cutaway to the Interior of the Sun. Credit: NASA
So, if you could connect the convective zone to the solar core, you’d be able to keep mixing up the material in the Sun. The core of the Sun would be able to efficiently fuse all the hydrogen in the star.
Sound crazy? Interestingly, this already happens in our Universe. For red dwarf stars with less than 35% the mass of the Sun, their convective zones connect directly to the core of the star. This is why these stars can last for hundreds of billions and even trillions of years. They will efficiently use up all the hydrogen in the entire star thanks to the mixing of the convective zone. If we could create a method to break through the radiative zone and get that fresh hydrogen into the core of the Sun, we could keep basking in its golden tanning rays for well past its current expiration date.
I never said it would be easy. It would take stellar engineering at a colossal scale to overcome the equilibrium of the star. A future civilization with an incomprehensible amount of energy and stellar engineering ability might be able to convert our one star into a collection of fully convective red dwarf stars. And these could sip away their hydrogen for trillions of years.
Tell us in the comments on how you think we should go about it. My money is on giant ‘magic bullet’ blender” or a perhaps a Dyson solar juicer.
Who knows what the future holds for our Sun? Dr. Mark Morris, a professor of astronomy at UCLA sure knows. Professor Morris sat down with us to let us know what we’re in for over the next few billions years.
“Hi, I’m Professor Mark Morris. I’m teaching at UCLA where I also carry out my research. I work on the center of the galaxy and what’s going on there – in this fabulous arena there, and on dying stars – stars that have reached the end of their lifetime and are putting on a display for us as they do so.”
What is the future of our sun?
“Well, there’s every expectation that in about 5 billion more years, that our sun will swell up to become a red giant. And then, as it gets larger and larger, it will eventually become what’s called an asymptotic giant branch star – a star whose radius is just under the distance between the sun and the Earth – one astronomical unit in size. So the Earth will be literally skimming the surface of the red giant sun when it’s an asymptotic giant branch star.”
“A star that big is also cool because they’re cold – red hot versus blue hot or yellow hot like our sun. Because it’s cold, a red giant star at its surface layers can keep all of its elements in the gas phase. So some of the heavier elements – the metals and the silicates – condense out as small dust grains, and when these elements condense out as solids, then radiation pressure from this very luminous giant star pushes the dust grains out. That may seem like a minor issue, but in fact these dust grains carry the gas with them. And so the star literally expels its atmosphere, and goes from a red giant star to a white dwarf, when finally the core of the star is exposed. Now, as it’s doing this, that hot core of the star is still very luminous and lights up through a fluorescent process, this out-flowing envelope, this atmosphere that was once a star, and that’s what produces these beautiful displays that are called planetary nebulae.”
“Now, planetary nebulae can be these beautiful round, spherical objects, or they can be bipolar, which is one of the mysteries that we’re working here is trying to understand why, at some stage, a star suddenly becomes axisymmetric – in other words, is sending out is’s atmosphere in two diametrically opposed directions predominantly, rather than continuing to lose mass spherically.”
Planetary Nebula M2-9 (Credit: Bruce Balick (University of Washington), Vincent Icke (Leiden University, The Netherlands), Garrelt Mellema (Stockholm University), and NASA)
“We can’t invoke rotation of the star – that would be one way to get a preferred axis, but stars don’t rotate fast enough. If you take the sun and let it expand to become a red giant, then by the conservation of angular momentum, it literally won’t be spinning at all. It’ll be spinning so slowly that it’ll literally have no effect. So we can’t invoke spin, so there must be something going on deep down inside the star, that when you finally expose some rapidly spinning core, it can have an effect.”
“Or, all of the stars that we see as planetary nebula can have binary companions, that could be massive planets or relatively low mass stars that themselves can impose an angular momentum orientation on the system. This is in fact an idea that I’ve been championing for decades now, and it has some traction. There’s a lot of planetary nebula nuclei, the white dwarves, that seem to have companions near them that are suspect for having been responsible for helping strip the atmosphere of the mass-losing red giant star but also providing a preferred axis along which the ejected matter can flow.”
Once our own Sun has consumed all the hydrogen fuel in its core, it too will reach the end of its life. Astronomers estimate this to be a short 7 billion years from now. For a few million years, it will expand into a red giant, puffing away its outer layers. Then it’ll collapse down into a white dwarf and slowly cool down to the background temperature of the Universe.
I’m sure you know that some other stars explode when they die. They also run out of fuel in their core, but instead of becoming a red giant, they detonate in a fraction of a second as a supernova.
So, what’s the big difference between stars like our Sun and the stars that can explode as supernovae?
Mass. That’s it.
Supernova progenitors – these stars capable of becoming supernovae – are extremely massive, at least 8 to 12 times the mass of our Sun. When a star this big runs out of fuel, its core collapses. In a fraction of a second, material falls inward to creating an extremely dense neutron star or even a black hole. This process releases an enormous amount of energy, which we see as a supernova.
If a star has even more mass, beyond 140 times the mass of the Sun, it explodes completely and nothing remains at all. If these other stars can detonate like this, is it possible for our Sun to explode?
Could there be some chain reaction we could set off, some exotic element a rare comet could introduce on impact, or a science fiction doomsday ray we could fire up to make the Sun explode?
Nope, quite simply, it just doesn’t have enough mass. The only way this could ever happen is if it was much, much more massive, bringing it to that lower supernovae limit.
In other words, you would need to crash an equally massive star into our Sun. And then do it again, and again.. and again… another half dozen more times. Then, and only then would you have an object massive enough to detonate as a supernova.
We don’t have to worry about our sun exploding into a supernova.
Now, I’m sure you’re all resting easy knowing that solar detonation is near the bottom of the planetary annihilation list. I’ve got even better news. Not only will this never happen to the Sun, but there are no large stars close enough to cause us any damage if they did explode.
A supernova would need to go off within a distance of 100 light-years to irradiate our planet.
According to Dr. Phil Plait from Bad Astronomy, the closest star that could detonate as a supernova is the 10 solar mass Spica, at a distance of 260 light-years. No where near close enough to cause us any danger.
So don’t worry about our Sun exploding or another nearby star going supernova and wiping us out. You can put your feet up and relax, as it’s just not going to happen.
The new nova is located in Delphinus alongside the familiar Summer Triangle outlined by Deneb, Vega and Altair. This may shows the sky looking high in the south for mid-northern latitudes around 10 p.m. local time in mid-August. The new object is ideally placed for viewing. Stellarium
Looking around for something new to see in your binoculars or telescope tonight? How about an object whose name literally means “new”. Japanese amateur astronomer Koichi Itagaki of Yamagata discovered an apparent nova or “new star” in the constellation Delphinus the Dolphin just today, August 14. He used a small 7-inch (.18-m) reflecting telescope and CCD camera to nab it. Let’s hope its mouthful of a temporary designation, PNVJ20233073+2046041, is soon changed to Nova Delphini 2013!
This map shows Delphinus and Sagitta, both of which are near the bright star Altair at the bottom of the Summer Triangle. You can star hop from the top of Delphinus to the star 29 Vulpeculae and from there to the nova. Or you can point your binoculars midway between Eta Sagittae and 29 Vul. The “5.7 star” is magnitude 5.7. Stellarium
Several hours later it was confirmed as a new object shining at magnitude 6.8 just under the naked eye limit. This is bright especially considering that nothing was visible at the location down to a dim 13th magnitude only a day before discovery. How bright it will get is hard to know yet, but variable star observer Patrick Schmeer of Germany got his eyes on it this evening and estimated the new object at magnitude 6.0. That not only puts it within easy reach of all binoculars but right at the naked eye limit for observers under dark skies. Wow! Since it appears to have been discovered on day one of the outburst, my hunch is that it will brighten even further.
Here’s a reverse “black stars on white” map some observers prefer for greater clarity. Stars are shown to 9th magnitude. Tycho visual magnitudes shown for 4 stars near the nova. The nova’s precise position is RA 20 h 23′ 31″, Dec. +20 deg. 46′. Created with Chris Marriott’s SkyMap
The only way to know is to go out for a look. I’ve prepared a couple charts you can use to help you find and follow our new guest. The charts show stars down to about 9th magnitude, the limit for 50mm binoculars under dark skies. The numbers on the chart are magnitudes (with decimals omitted, thus 80 = 8.0 magnitude) so you can approximate its brightness and follow the ups and downs of the star’s behavior in the coming nights.
Despite the name, a nova is not truly new but an explosion on a star otherwise too faint for anyone to have noticed. A nova occurs in a close binary star system, where a small but extremely dense and massive (for its size) white dwarf grabs hydrogen gas from its closely orbiting companion. After swirling about in a disk around the dwarf, it’s funneled down to the star’s 150,000 degree F surface where gravity compacts and heats the gas until it detonates like a bazillion thermonuclear bombs. Suddenly, a faint star that wasn’t on anyone’s radar vaults a dozen magnitudes to become a standout “new star”.
Model of a nova in the making. A white dwarf star pulls matter from its bloated red giant companion into a whirling disk. Material funnels to the surface where it later explodes. Credit: NASA/CXC/M. Weiss
Novae can rise in brightness from 7 to 16 magnitudes, the equivalent of 50,000 to 100,000 times brighter than the sun, in just a few days. Meanwhile the gas they expel in the blast travels away from the binary at up to 2,000 miles per second. This one big boom! Unlike a supernova explosion, the star survives, perhaps to “go nova” again someday.
Closer view yet of the apparent nova showing a circle with a field of view of about 2 degrees. Stellarium
I’ll update with links to other charts in the coming day or two, so check back.
The Hubble Space Telescope is going to be used to settle an argument. It’s a conflict between computer models and what astronomers are seeing in a group of stars in 47 Tucanae.
White dwarfs — the dying embers of stars who have burnt off all their fuel — are cooling off slower than expected in this southern globular cluster, according to previous observations with the telescope’s Wide Field Camera and Advanced Camera for Surveys.
Puzzled astronomers are now going to widen that search in 47 Tucanae (which initially focused on a few hundred objects) to 5,000 white dwarfs. They do have some theories as to what might be happening, though.
White dwarfs, stated lead astronomer Ryan Goldsbury from the University of British Columbia, have several factors that chip in to the cooling rate:
The Hubble Space Telescope. Image credit: NASA, tweaked by D. Majaess.
– High-energy particle production from the white dwarfs;
– What their cores are made up of;
– What their atmospheres are made up of;
– Processes that bring energy from the core to the surface.
Somewhere, somehow, perhaps one of those factors is off.
This kind of thing is common in science, as astronomers create these programs according to the best educated guesses they can make with respect to the data in front of them. When the two sides don’t jive, they do more observations to refine the model.
“The cause of this difference is not yet understood, but it is clear that there is a discrepancy between the data and the models,” stated the Canadian Astronomical Society (CASCA) and the University of British Columbia in a press release.
Since the white dwarfs are in a cluster that presumably formed from the same cloud of gas, it allows astronomers to look at a group of stars at a similar distance and to determine the distribution of masses of stars within the cluster.
“Because all of the white dwarfs in their study come from a single well-studied star cluster, both of these bits of information can be independently determined,” the release added.
You can read the entire article on the previous Hubble research on 47 Tucanae at the Astrophysical Journal.
Today’s announcement took place during the annual meeting of CASCA, which is held this year in Vancouver.
An artist's conception of the SS Cygni system, with a red dwarf star's material being pulled on to a nearby white dwarf. Credit: Bill Saxton, NRAO/AUI/NSF
If you’re a semi-serious amateur astronomer, chances are you’ve heard of a variable pair of stars called SS Cygni. When you watch the system for long enough, you’re rewarded with a brightness outburst that then fades away and then returns, regularly, over and over again.
Turns out this bright pair is even closer to us than we imagined — 370 light-years away, to be precise.
Before we get into how this was discovered, a bit of background on what SS Cygni is. As the name of the system implies, it’s in the constellation of Cygnus (the Swan). The pair consists of a cooling white dwarf star that is locked in a 6.6-hour orbit with a red dwarf.
The white dwarf’s gravity, which is much stronger than that of the red dwarf, is bleeding material from its neighbor. This interaction causes outbursts — on average, about once every 50 days.
Previously, the Hubble Space Telescope put the distance to these stars much further away, at 520 light-years. But that caused some head-scratching among astronomers.
Hubble Against Earth’s Horizon (1997)
“That was a problem. At that distance, SS Cygni would have been the brightest dwarf nova in the sky, and should have had enough mass moving through its disk to remain stable without any outbursts,” stated James Miller-Jones, of the Curtin University node of the International Centre for Radio Astronomy Research in Perth, Australia.
Astronomers call SS Cygni a dwarf nova. When comparing it to similar systems, astronomers said the outbursts happen as matter changes its flow speed through the disc of material surrounding the white dwarf.
“At high rates of mass transfer from the red dwarf, the rotating disk remains stable, but when the rate is lower, the disk can become unstable and undergo an outburst,” stated the National Radio Astronomy Observatory. So what was happening?
A star’s distance is measured by observing a slight shift in position that occurs, from Earth’s perspective, on opposite sides of our planet’s orbit. Credit: Bill Saxton, NRAO/AUI/NSF
To again look at the distance of the star, astronomers used two sets of radio telescopes, the Very Large Baseline Array and the European VLBI Network. Each set has a bunch of telescopes working together as an interferometer, allowing for precise measurements of star distances.
Scientists then took measurements at opposite ends of the Earth’s orbit, using the planet itself as a tool. By measuring the star’s distance at opposite sides of the orbit, we can calculate its parallax or apparent movement in the sky from the perspective of Earth. It’s an old astronomical tool used to pin down distances, and still works.
“This is one of the best-studied systems of its type, but according to our understanding of how these things work, it should not have been having outbursts. The new distance measurement brings it into line with the standard explanation,” stated Miller-Jones.
And where did Hubble go wrong? Here’s the theory:
“The radio observations were made against a background of objects far beyond our own Milky Way Galaxy, while the Hubble observations used stars within our galaxy as reference points,” NRAO stated. “The more-distant objects provide a better, more stable, reference.”
Hubble image of SNR 0519, the remains of a Type Ia supernova in the Large Magellanic Cloud
Stars like our Sun can last for a very long time (in human terms, anyway!) somewhere in the neighborhood of 10-12 billion years. Already over 4.6 billion years old, the Sun is entering middle age and will keep on happily fusing hydrogen into helium for quite some time. But eventually even stars come to the end of their lives, and their deaths are some of the most powerful — and beautiful — events in the Universe.
The wispy, glowing red structures above are the remains of a white dwarf in the neighboring Large Magellanic Cloud 150,000 light-years away. Supernova remnant SNR 0519 was created about 600 years ago (by our time) when a star like the Sun, in the final stages of its life, gathered enough material from a companion to reach a critical mass and then explode, casting its outer layers far out into space to create the cosmic rose we see today.
As the hydrogen material from the star plows outwards through interstellar space it becomes ionized, glowing bright red.
SNR 0519 is the result of a Type Ia supernova, which are the result of one white dwarf within a binary pair drawing material onto itself from the other until it undergoes a core-collapse and blows apart violently. The binary pair can be two white dwarfs or a white dwarf and another type of star, such as a red giant, but at least one white dwarf is thought to always be the progenitor.
A recent search into the heart of the remnant found no surviving post-main sequence stars, suggesting that SNR 0519 was created by two white dwarfs rather than a mismatched pair. Both stars were likely destroyed in the explosion, as any non-degenerate partner would have remained.
Artist’s concept showing a dust disk around a binary system containing a white dwarf and a less-massive M (red) dwarf companion. (P. Marenfeld and NOAO/AURA/NSF)
Even though NASA’s Wide-field Infrared Survey Explorer spacecraft — aka WISE — ran out of coolant in October 2010, bringing its infrared survey mission to an end, the data that it gathered will be used by astronomers for decades to come as it holds clues to some of the most intriguing and hard-to-find objects in the Universe.
Recently astronomers using WISE data have found evidence of a particularly curious disk of dust and gas surrounding a pair of stars — one a dim red dwarf and the other the remains of a dead Sun-sized star — a white dwarf. The origin of the gas is a mystery, since based on standard models of stellar evolution it shouldn’t be there… yet there it is.
The binary system (which has the easy-to-remember name SDSS J0303+0054) consists of a white dwarf and a red dwarf separated by a distance only slightly larger than the radius of the Sun — about 700,000 km — which is incredibly close for two whole stars. The stars orbit each other quickly too: once every 3 hours.
The stars are so close that the system is referred to as a “post-common envelope” binary, because at one point the outer material of one star expanded out far enough to briefly engulf the other completely in what’s called a “common envelope.” This envelope of material brought the stars even closer together, transferring stellar material between them and ultimately speeding up the death of the white dwarf.
The system was first spotted during the Sloan Digital Sky Survey (hence the SDSS prefix) and was observed with WISE’s infrared abilities during a search for dust disks or brown dwarfs orbiting white dwarf stars. To find both a red (M) dwarf star 40-50 times the mass of Jupiter and a disk of dust orbiting the white dwarf in this system was unexpected — in fact, it’s the only known example of a system like it.
The entire mass of the dust (termed an infrared excess) is estimated to be “equivalent to the mass of an asteroid a few tens of kilometers in radius” and extends out to about the same distance as Venus’ orbit — just over 108 million kilometers, or 0.8 AU.
Why is the dust so unusual? Because, basically, it shouldn’t even be there. At that distance from the white dwarf, positioned just out of reach (but not terribly far away at all) anything that was within that zone when the original Sun-sized star swelled into its red giant phase should have spiraled inwards, getting swallowed up by the expanding stellar atmosphere.
Such is the fate that likely awaits the inner planets of our own Solar System — including Earth — when the Sun reaches the final phases of its stellar life.
So this requires that there are other sources of the dust. According to the WISE science update, “One possibility is that it is caused by multiple asteroids that orbit further away and somehow are perturbed close to the binary and collide with each other. [Another] is that the red dwarf companion releases a large amount of gas in a stellar wind that is trapped by the gravitational pull of its more massive white dwarf companion. The gas then condenses and forms the dust disk that is observed.
“Either way, this new discovery provides an interesting laboratory for the study of binary star evolution.”
WISE launched into space on Dec. 14, 2009 on a mission to map the entire sky in infrared light with greatly improved sensitivity and resolution over its predecessors. From its polar orbit 525 kilometers (326 miles) in altitude it scanned the skies, collecting images taken at four infrared wavelengths of light. WISE took more than 2.7 million images over the course of its mission, capturing objects ranging from faraway galaxies to asteroids relatively close to Earth before exhausting the supply of coolant necessary to mask its own heat from its ultra-sensitive sensors.
Inset: Infrared images of SDSS J0303+0054. (NASA/JPL and John H. Debes et. al.)
Two white dwarfs similar to those in the system SDSS J065133.338+284423.37 spiral together in this illustration from NASA. Credit: D. Berry/NASA GSFC
Locked in a spiraling orbital embrace, the super-dense remains of two dead stars are giving astronomers the evidence needed to confirm one of Einstein’s predictions about the Universe.
A binary system located about 3,000 light-years away, SDSS J065133.338+284423.37 (J0651 for short) contains two white dwarfs orbiting each other rapidly — once every 12.75 minutes. The system was discovered in April 2011, and since then astronomers have had their eyes — and four separate telescopes in locations around the world — on it to see if gravitational effects first predicted by Einstein could be seen.
According to Einstein, space-time is a structure in itself, in which all cosmic objects — planets, stars, galaxies — reside. Every object with mass puts a “dent” in this structure in all dimensions; the more massive an object, the “deeper” the dent. Light energy travels in a straight line, but when it encounters these dents it can dip in and veer off-course, an effect we see from Earth as gravitational lensing.
Einstein also predicted that exceptionally massive, rapidly rotating objects — such as a white dwarf binary pair — would create outwardly-expanding ripples in space-time that would ultimately “steal” kinetic energy from the objects themselves. These gravitational waves would be very subtle, yet in theory, observable.
What researchers led by a team at The University of Texas at Austin have found is optical evidence of gravitational waves slowing down the stars in J0651. Originally observed in 2011 eclipsing each other (as seen from Earth) once every six minutes, the stars now eclipse six seconds sooner. This equates to a predicted orbital period reduction of about 0.25 milliseconds each year.*
“These compact stars are orbiting each other so closely that we have been able to observe the usually negligible influence of gravitational waves using a relatively simple camera on a 75-year-old telescope in just 13 months,” said study lead author J.J. Hermes, a graduate student at The University of Texas at Austin.
Based on these measurements, by April 2013 the stars will be eclipsing each other 20 seconds sooner than first observed. Eventually they will merge together entirely.
Although this isn’t “direct” observation of gravitational waves, it is evidence inferred by their predicted effects… akin to watching a floating lantern in a dark pond at night moving up and down and deducing that there are waves present.
“It’s exciting to confirm predictions Einstein made nearly a century ago by watching two stars bobbing in the wake caused by their sheer mass,” said Hermes.
As of early last year NASA and ESA had a proposed mission called LISA (Laser Interferometer Space Antenna) that would have put a series of 3 detectors into space 5 million km apart, connected by lasers. This arrangement of precision-positioned spacecraft could have detected any passing gravitational waves in the local space-time neighborhood, making direct observation possible. Sadly this mission was canceled due to FY2012 budget cuts for NASA, but ESA is moving ahead with developments for its own gravitational wave mission, called eLISA/NGO — the first “pathfinder” portion of which is slated to launch in 2014.
The study was submitted to Astrophysical Journal Letters on August 24. Read more on the McDonald Observatory news release here.
Inset image: simulation of binary black holes causing gravitational waves – C. Reisswig, L. Rezzolla (AEI); Scientific visualization – M. Koppitz (AEI & Zuse Institute Berlin)
*The difference in the eclipse time is noted as six seconds even though the orbital period decay of the two stars is only .25 milliseconds/year because of a pile-up effect of all the eclipses observed since April 2011. The measurements made by the research team takes into consideration the phase change in the J0651 system, which experiences a piling effect — similar to an out-of-sync watch — that increases relative to time^2 and is therefore a larger and easier number to detect and work with. Once that was measured, the actual orbital period decay could be figured out.
