TIGHTLY ORBITING a PULSAR
Astronomers discover planet made of diamond
by Ben Hirschler / Aug 25, 2011
Astronomers have spotted an exotic planet that seems to be made of diamond racing around a tiny star in our galactic backyard. The new planet is far denser than any other known so far and consists largely of carbon. Because it is so dense, scientists calculate the carbon must be crystalline, so a large part of this strange world will effectively be diamond. “The evolutionary history and amazing density of the planet all suggest it is comprised of carbon — i.e. a massive diamond orbiting a neutron star every two hours in an orbit so tight it would fit inside our own Sun,” said Matthew Bailes of Swinburne University of Technology in Melbourne. Lying 4,000 light years away, or around an eighth of the way toward the center of the Milky Way from the Earth, the planet is probably the remnant of a once-massive star that has lost its outer layers to the so-called pulsar star it orbits. Pulsars are tiny, dead neutron stars that are only around 20 kilometers (12.4 miles) in diameter and spin hundreds of times a second, emitting beams of radiation. In the case of pulsar J1719-1438, the beams regularly sweep the Earth and have been monitored by telescopes in Australia, Britain and Hawaii, allowing astronomers to detect modulations due to the gravitational pull of its unseen companion planet.
The measurements suggest the planet, which orbits its star every two hours and 10 minutes, has slightly more mass than Jupiter but is 20 times as dense, Bailes and colleagues reported in the journal Science on Thursday. In addition to carbon, the new planet is also likely to contain oxygen, which may be more prevalent at the surface and is probably increasingly rare toward the carbon-rich center. Its high density suggests the lighter elements of hydrogen and helium, which are the main constituents of gas giants like Jupiter, are not present. Just what this weird diamond world is actually like close up, however, is a mystery. “In terms of what it would look like, I don’t know I could even speculate,” said Ben Stappers of the University of Manchester. “I don’t imagine that a picture of a very shiny object is what we’re looking at here.”
DIAMONDS are FOREVER
by Irene Klotz / Aug 25, 2011
Astronomers have found the remains of a once-massive star, now transformed into a solid diamond five times bigger than Earth. The object circles a pulsing companion star about 4,000 light years from Earth in the constellation Serpens (The Snake), which lies about one-eighth of the way toward the center of the Milky Way galaxy. Astronomers noticed that the steady pulses of energy coming from the star, known as J1719-1438, were regularly and minutely disturbed, a phenomenon caused by the gravitational tug of another, smaller circling object. By measuring the pattern, scientists were able to figure out how far away the second object circles and its mass, leading to the realization that they had found a bizarre binary system, with one partner reduced to a diamond core. “In this case, something with the mass of our sun has evolved to be something the mass of a planet — quite extraordinary,” astronomer Michael Keith, with the Australia Telescope National Facility, wrote in an email to Discovery News. The companion to J1719-1438 never got big enough to produce elements much heavier than carbon, so after its lighter-weight hydrogen and helium were stripped away that would leave a solid core of carbon — diamond. “Due to the immense pressure, the carbon will be in a dense crystal-like structure, although much more closely packed than in a diamond on Earth,” Keith said.
The system is now stable, with no evidence that it will change for billions of years. “Of course, this also means that it could well have been around for a long time, just waiting for us to find it. Since it’s likely to last for longer than the Earth or the sun, I would say that in this case, a diamond really is forever,” Keith said. The diamond planet was found as part of an ongoing search for pulsating stars, known as pulsars, which scientists like to use as probes. “We’d like to find a pulsar with a black hole companion,” Michael Kramer, director of the Max Planck Institute for Radio Astronomy in Bonn, Germany, told Discovery News. “It’s the exotic case that tell us most about the laws of physics and what’s going on in the universe.”
STRIPPED to the CORE
Pulsar strips a white dwarf, leaves a Jupiter-sized diamond
by John Timmer / August 25 2011
Neutron stars form from the core of a collapsing star and, as the supernova dissipates, often rotate rapidly, creating a pulsar. In less than a million years, however, their strong magnetic fields act as a brake, slowing them down considerably. In some cases, however, the neutron star will have a nearby companion, and its gravity is sufficient to start stripping mass off it. As the process continues, the neutron star will spin back up, creating what’s called a millisecond pulsar. In most cases, these companions are still around, visible as a bright star locked in an orbital embrace with a pulsar. Now, researchers have spotted one where the star is still there, but not visible—the neutron star has stripped it down to a crystaline core the size of Jupiter.
The system in question, which has the catchy name PSR J1719−1438, was identified in a recent survey for pulsars. Careful timing observations revealed the influence of a nearby companion—very nearby, given that it orbited the neutron star with a period of only a bit over two hours. Given the orbital information and the typical mass of a neutron star, the authors were able to estimate that the orbiting body has a mass somewhere around that of Jupiter. But that mass must be highly compact; otherwise, given the limited distance between the two, the neutron star would end up gravitationally disrupting its companion. The same goes for a helium-rich white dwarf star. The only thing that the authors calculate could fit into this uncomfortably close orbital configuration is a carbon white dwarf. So, they conclude that the “planet” orbiting the neutron star is simply the core of its previous stellar companion, stripped of most of its mass through the process that spun up the pulsar. And, in the last sentence of the paper, they drop a bit of a bombshell: “The chemical composition, pressure and dimensions of the companion make it certain to be crystallized (i.e., diamond).”
About 30 percent of the millisencond pulsars we know about don’t have a stellar companion, which raises the possibility that there are other Jupiter-mass diamonds out there awaiting our discovery. However, other fates are possible; a bit closer, and the companion star would have been devoured completely, leaving no remnant at all. And, in at least one case, a companion star seems to have been torn apart in a way converting it into a disk that has formed three planets that now orbit the neutron star. With further observations, we should get a better sense of how common these odd companions are—and possibly find something else that’s even stranger.
Science, 2011. DOI: 10.1126/science.1208890.
A diamond as big as a planet
by David Shiga / 25 August 2011
Cruising through the Milky Way in your reconnaissance craft, your sensors pick up a powerful radio beacon. Altering your course to take a closer look, you find not a ship in distress, but an ultradense sphere of neutrons, packing a sun’s worth of mass into something the size of a city. This dead remnant of a star glows red like a hot ember, and is spinning 173 times per second, emitting powerful radio beams that sweep across the sky as it rotates. While such pulsars are striking, they are nothing out of the ordinary, so you are about to resume your original course when your eye catches something sparkling near the dim red glow. A closer look reveals it to be an orb with the mass of Jupiter and about half as wide. Sensors indicate it’s made of – wait, this can’t be right – diamond! Your instruments don’t lie. You’ve just stumbled upon a 1031-carat diamond.
Fanciful as it may sound, a team led by Matthew Bailes of Swinburne University of Technology in Melbourne, Australia may have made a similar discovery – via telescope, not a starship. Their radio survey of the sky detected the pulsar in December 2009, using the CSIRO Parkes radio telescope in New South Wales, Australia. A month later, follow-up observations with the Lovell radio telescope in Cheshire, UK, revealed periodic variations in the pulsar’s signals, indicating the existence of an orbiting companion with the mass of a planet.
That in itself was a rare find: of the 1800 or so pulsars known, only two had previously been found to harbour planets. Further analysis pointed to an even more astonishing possibility – a diamond planet. The variations in the pulsar’s signals, which stem from the planet’s gravity tugging on the pulsar, revealed that the planet’s mass is roughly equal to Jupiter’s and that it orbits the pulsar at a distance of 600,000 kilometres, 1.5 times the distance of the moon from Earth.
The latter point is crucial. The planet orbits so close to the pulsar that it skirts the danger zone within which the star’s gravity would rip it apart. Wait a minute, though. If it were a gas giant the size of Jupiter, part of its atmosphere would actually be inside the gravitational destruction zone, and the planet would not have survived long enough for Bailes’s team to detect it. So it must be less than about 60,000 kilometres in diameter, roughly 40 per cent of Jupiter’s width. That in turn means it is much more compact than Jupiter, which has an average density only slightly greater than water. The extremely fast rotation of the pulsar supports this conclusion. Pulsars that rotate many times each second are thought to spin up to such tremendous speeds as a result of stealing matter from a companion star. But there is no sign of such a massive companion today, so the planet is likely all that’s left of a star that was whittled down by the pulsar.
The core of a stripped down star would be mostly carbon, with a dash of oxygen. With the mass of Jupiter, such an object would be under high pressure because of its own gravity. And this would cause it to crystallise – most likely into diamond, just as carbon does deep inside the Earth. If it is a diamond, does the planet glitter like an Earthly gem? “It’s highly speculative, but if you shine a light on it, I can’t see any reason why it wouldn’t sparkle like a diamond,” says Travis Metcalfe of the National Center for Atmospheric Research in Boulder, Colorado. He previously found a white dwarf – the remnant of an old star – with a carbon-crystal core that was under higher pressure than the new planet, producing a crystalline structure distinct from diamond. Moshe Mosbacher, president of the Diamond Dealers Club in New York says he has “no clue” how much a diamond of this size would fetch, without first knowing its quality. But he is intrigued. “If there’s some way to transport it to New York and cut it, it doesn’t make a difference if it’s from inner space or outer space.”
LIQUID DIAMOND OCEANS (POSSIBLE) ON URANUS, NEPTUNE
by Eric Bland / Jan 15, 2010
Oceans of liquid diamond, filled with solid diamond icebergs, could be floating on Neptune and Uranus, according to a recent article in the journal Nature Physics. The research, based on the first detailed measurements of the melting point of diamond, found diamond behaves like water during freezing and melting, with solid forms floating atop liquid forms. The surprising revelation gives scientists a new understanding about diamonds and some of the most distant planets in our solar system. “Diamond is a relatively common material on Earth, but its melting point has never been measured,” said J. H. Eggert of Lawrence Livermore National Laboratory in Livermore, Calif. “You can’t just raise the temperature and have it melt, you have to also go to high pressures, which makes it very difficult to measure the temperature.”
Other groups, notably scientists from Sandia National Laboratories, successfully melted diamond years ago, but they were unable to measure the pressure and temperature at which the diamond melted. Diamond is an incredibly hard material. That alone makes it difficult to melt. But diamond has another quality that makes it even harder to measure its melting point. Diamond doesn’t like to stay diamond when it gets hot. When diamond is heated to extreme temperatures it physically changes, from diamond to graphite. The graphite, and not the diamond, then melts into a liquid. The trick for the scientists was to heat the diamond up while simultaneously stopping it from transforming into graphite.
Eggert and his colleagues took a small, natural, clear diamond, about a tenth of a carat by weight and half a millimeter thick, and blasted it with lasers at ultrahigh pressures like those found on gas giants like Neptune and Uranus. The scientists liquefied the diamond at pressures 40 million times greater than what a person feels when standing at sea level on Earth. From there they slowly reduced the temperature and pressure. When the pressure dropped to about 11 million times the atmospheric pressure at sea level on Earth and the temperature dropped to about 50,000 degrees, solid chunks of diamond began to appear. The pressure kept dropping, but the temperature of the diamond remained the same, with more and more chunks of diamond forming. Then the diamond did something unexpected. The chunks of diamond didn’t sink. They floated. Microscopic diamond ice burgs floated in a tiny sea of liquid diamond. The diamond was behaving like water.
With most materials, the solid state is more dense than the liquid state. Water is an exception to that rule; when water freezes, the resulting ice is actually less dense than the surrounding water, which is why the ice floats and fish can survive a Minnesota winter. An ocean of diamond could help explain the orientation of Uranus’ and Neptune’s magnetic field as well, said Eggert. Roughly speaking, the Earth’s magnetic poles match up with the geographic poles. The magnetic and geographic poles on Uranus and Neptune do not match up; in fact, they can be up to 60 degrees off of the north-south axis. If Earth’s magnetic field were that far off it would place the magnetic north pole in Texas instead of off a Canadian island. A swirling ocean of liquid diamond could be responsible for the discrepancy.
Up to 10 percent of Uranus and Neptune is estimated to be made from carbon. A huge ocean of liquid diamond in the right place could deflect or tilt the magnetic field out of alignment with the rotation of the planet. The idea that there are oceans of liquid diamond on Neptune and Uranus is not a new idea, said Tom Duffy, a planetary scientist at Princeton University. The new Nature Physics article makes diamond oceans “look more and more plausible,” said Duffy. More research on the composition of Neptune and Uranus is needed before a truly definitive conclusion can be made, however, and this kind of research is very difficult to conduct. Scientists can either send spacecraft to these planets, or they can try to simulate the conditions on Earth. Both options require years of preparation, expensive equipment, and are subject to some of the toughest environments in the universe.
Astronomers have just solved a decade-old mystery that explains the unusual behavior of a neutron star — the dense, hot corpse left behind after a massive stellar explosion — at the center of the Cassiopeia A supernova remnant. It wasn’t the X-rays streaming from the center of the supernova remnant that astronomers found puzzling. It’s why the beams weren’t pulsating as expected. Now the scientists know why: The neutron star is covered with a thin atmosphere of carbon, which acts like a giant bulb to smooth light in all directions. The findings help to illustrate the extreme nature of these entities. “The carbon is unique,” Wynn Ho, a researcher with the University of Southampton in the United Kingdom, told Discovery News. “The neutron stars that have been detected with atmosphere have evolved with hydrogen, and that’s what we’d expect because hydrogen is the most abundant element in the universe.” Scientists believe the neutron star in Cassiopeia A is so young and hot that in addition to fusing hydrogen to form helium, the surface of the star is fusing helium into carbon.
Computer models show the carbon veil to be extremely thin — up to just four inches thick — due to the immense gravitational pull of the neutron star, which is about one billion times stronger than Earth’s gravity. Though the shroud is as dense as diamonds, the star’s 3.6 million-degree Fahrenheit temperature would keep the atmosphere gaseous. “It’s incredibly hot, so it’s still a gas,” said Peter Edmonds, with the Chandra X-ray Center at the Harvard-Smithsonian Center for Astrophysics. irect observations of the neutron star’s atmosphere are not possible with today’s technology, given its distance and other factors, but scientists are on the lookout for other young neutron stars that may also sport carbon shells. Being based on computer models, the finding isn’t ironclad, added Edmonds, “but it’s a strong case.” Cassiopeia A’s neutron star also serves as proverbial lab rat for physicists wondering what sort of exotic matter exists inside. “We’re using it to study the neutron star interior to determine whether its interior is made of superconducting material or quark matter. You can determine this based on its temperature and its age,” Ho said. “Any exotic matter will determine how rapidly it cools over time.”