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In the Sky with Diamonds

The idea of a planet around a pulsar is so bizarre that we often forget that three planets around the pulsar PSR B1257+12 were the first exoplanets ever detected. This pulsar is the remnant of a once massive star in the constellation Virgo that became a supernova, and the planets there — detected by Alex Wolszczan (Penn State) — were the first new planets discovered since the era when Clyde Tombaugh was putting the blink comparator through its paces at Lowell Observatory, an effort that led to the discovery of Pluto in 1930. And these are tiny worlds at that. A newly found fourth planet in the B1257+12 system is thought to be no more than one-fifth the mass of Pluto itself. We can find worlds like this because the beam of electromagnetic radiation pulsars emit is extraordinarily regular, making planetary signatures apparent.

Now another pulsar — PSR J1719-1438, some 4,000 light years away in the constellation Serpens (the Snake) — is in the news because of the discovery that its own pulses are being affected by the gravitational pull of a small planet. What we are learning about the new planet is highly interesting. It is slightly more massive than Jupiter, and orbits the pulsar at a distance of about 600,000 kilometers, racing around its primary in a scant two hours and ten minutes. The pulsar rotates more than 10,000 times per minute and has a mass about 1.4 times that of our Sun, but is only 20 kilometers in radius. At 600,000 kilometers out, a planet larger than 60,000 kilometers (five times Earth’s diameter) would be pulled apart by the pulsar’s gravity.

This must be, then, a small planet with a great deal of mass, which is why this story stands out. For what Matthew Bailes (Swinburne University of Technology, Melbourne) and colleagues are reporting is a planet that may itself be the remains of a massive star. The pulsar and its companion are close enough that the planet must in fact be what’s left of a white dwarf that has lost over 99.9 percent of its original mass. And that leaves us with an interesting relic, a remnant of carbon and oxygen at such high density that the star may be made largely of diamond.

The paper on this work states the matter clearly:

PSR J1719−1438 demonstrates that special circumstances can conspire during binary pulsar evolution that allows neutron star stellar companions to be transformed into exotic planets unlike those likely to be found anywhere else in the Universe. The chemical composition, pressure and dimensions of the companion make it certain to be crystallized (ie diamond).

Image: Artistic reproduction of an extrasolar planet around a pulsar. Copyright : Paris Observatory/UF.

Most of the mass of the so-called ‘diamond planet’ would have been drawn toward the pulsar. Interestingly enough, very fast-spinning pulsars like this one — astronomers call them millisecond pulsars — normally have companions of some kind. In fact, as many as 70 percent of them do. According to this CSIRO news release, some astronomers believe that such companions, when burning as a star, would be responsible for transferring matter to the pulsar and spinning it up to its high speed. The result over time: A millisecond pulsar keeping company with a white dwarf.

This configuration of pulsar and white dwarf makes sense, but finding former white dwarfs that have survived destruction only to become crystalline planets is not likely to be common:

“The ultimate fate of the binary is determined by the mass and orbital period of the donor star at the time of mass transfer. The rarity of millisecond pulsars with planet-mass companions means that producing such exotic planets is the exception rather than the rule, and requires special circumstances,” said Dr. Benjamin Stappers (University of Manchester).

We should learn a great deal more about pulsars from the project this work grew out of, a search for pulsars that is the largest and most sensitive of its type ever attempted. It will doubtless identify more pulsar planets, and probably more intriguing circumstellar disks of the kind already found around the pulsar 4U 0142+61. Planets, as we’re realizing more and more, seem to find myriad ways to form even after events as massive as a supernova. The paper is Bailes et al., “Transformation of a Star into a Planet in a Millisecond Pulsar Binary,” published online in Science Express August 25 2011 (abstract).


Comments on this entry are closed.

  • Adam August 26, 2011, 8:18

    Dead heart of a star as a diamond… What a thought! Reminds me of a certain nursery rhyme…
    Twinkle, twinkle little star
    I no longer wonder what you are.
    You’re a diamond in the sky
    Around a pulsar up so high.

  • Paul Gilster August 26, 2011, 8:42

    Well said, Adam! In the exoplanet hunt, it seems that wonders never cease.

  • ljk August 26, 2011, 9:37

    If there is a world with 1/5th the mass of Pluto, can we really call it a planet no matter what system it resides in? Luna is bigger than Pluto and all four of its known moons combined.

    We keep talking about wanting to find other Earths, but how dull is that? We should be seeking the exotica the Universe has to offer, of which we are only now getting real hints at. An entire planet made of diamond that was once a star? Tell me that isn’t worth sending an expedition to. Imagine the uses a galactic-spanning society could make of such a place.

  • Mike August 26, 2011, 10:04

    That’s for sure Paul! The more we look the more we find!

    In a previous post I commented about the possible definitions of what a “dead” star could be. I’m pleased to learn about a new one. Stripped of mass down to a diamond core and re-incarnated as a planet. Exotic.

    What other exoplanet wonders await? We just need to fund and build the equipment. The kind of equipment that could reveal bio-markers on nearby exoplanets that is. DAVINCI, for example could be done for under 1.5 billion. There are other similar proposals too. Funding, funding.

  • ljk August 26, 2011, 10:11

    By the way, I was being somewhat facetious when I said previously that finding an alien version of Earth would be dull. Obviously discovering planets in other solar systems that resemble ours would be “fascinating”, to quote a certain famous Vulcan who often boldly went where no man/one had gone before. They would be major indicators that life is not unique to our globe, among other things crucial to our knowledge of the Cosmos.

    However, when I hear the constant desire by those both professional and in the general public focusing on finding an analogue to Earth, I keep thinking of Stanislaw Lem’s quote from Solaris that humans don’t want other planets, they want mirrors.

    In addition, it also seems to keep being stepped over that any Earthlike worlds will probably have native life forms and likely complex ones at that.

    Even if we could colonize such planets without any major restructuring, should we? Or should we seek out barren places and terraform them? All of this assumes our star-faring descendants will actually want to live on a planet rather than just visit for exploration or resources. This also assumes that the ones who will be passengers on a starship will only be as human as we are now, or that the ships themselves are not intelligent beings.

  • Dave August 26, 2011, 10:49

    Here’s the researchers’ video (we’re getting plenty of user-comments on it on our YouTube channel):

  • ROCA August 26, 2011, 12:41

    The more we learn about exoplanets the more we understand that Earth itself is an unique world, a very rare place in the Universe.

  • Antonio August 26, 2011, 15:26

    Ma un pianeta così strano e bizzarro, se fosse posto nella zona abitabile della sua stella(evidentemente, non attorno ad una “pulsar”) avrebbe la possibilità di supportare qualche forma di vita? Potrebbe avere un’atmosfera, e qualche liquido, in superficie?

    Mi scuso se la domanda può sembrare eccessivamente irrealistica, ma considerando che ogni nuova scoperta, ci fa scoprire sempre nuove “meraviglie” cosmiche, del tutto inaspettate, ho pensato di porre a voi lettori di questo “blog”, questa mia domanda…

    Saluti da Antonio.

  • Paul Gilster August 26, 2011, 15:46

    Antonio’s comment (via Google Translate):

    But a world so strange and bizarre, if it were placed in the habitable zone of its star (obviously, not around a “pulsar”) would be able to support some form of life? Could have an atmosphere, and some liquid on the surface?

    I apologize if the question may seem too unrealistic, but considering that every new discovery, we discover always new “wonders” cosmic, completely unexpected, I thought I’d ask you readers of this “blog”, my question …

    Greetings from Antonio.

  • Eric W. Davis August 26, 2011, 15:57

    Gosh, I hope De Beers doesn’t find out about this. They control the world diamond market. :-)

  • Paul Gilster August 26, 2011, 17:25

    No kidding! But imagine what happens to the world diamond market if DeBeers could pull this one in. How many carats are we talking about here? ;-)

  • Phil August 26, 2011, 18:57

    Paul, according to google:

    mass of Jupiter / (1 carat) = 9.4935 × 10^30

  • Daniel Suggs August 26, 2011, 19:07

    Paul, I may be late with this suggestion, but I think we should name this planet/star Lucy. As in ‘Lucy in the sky with diamonds’. Just sayin’..

  • Rob Henry August 26, 2011, 19:15

    Everyone seems distracted by the fascinating chemical and formation aspects of this planet. Am I the only one who notes that the prediction that the high density allowing it to remain just above the Roche limit, and the very tight orbit means that, if it had a very extensive atmosphere, the gas would be smeared right around the orbit in a dense confined smoke ring. When Larry Niven wrote “The Integral Trees” I thought that such a set up could never exist in reality, but here we might have found one already!

  • Paul Gilster August 26, 2011, 19:53

    I like ‘Lucy’ as the name, as Daniel suggests, and Phil’s carat ratio also looks promising. Diamonds are forever, as they say…

  • Interstellar Bill August 26, 2011, 20:25

    If Carl Sagan’s vaunted ‘Copernican Principle’ had the slightest validity,
    we would by now have found numerous Earth-type planets
    and even more nice, stable solar systems. There would have been a significant number of systems with TWO habitable planets.

    You know what actually happened:
    Hot Jupiters
    (some transiting visible stars biweekly,
    right before our noses all these centuries of astronomy)
    Chaotic Orbits
    Retrograde Planets
    The Styrofoam Planet
    The Black Planet
    The Diamond Planet
    andm Huzzah, Huzzah

    None of these were predicted by pre-1995 astronomy
    or ever appeared in science fiction.

    When it comes to our type of world, however, our planet-eager SF scenarios have been thawarted by pickings that are meager:
    The most relaxed category, a Goldilocks orbit in the water zone,
    has only a few tentative Kepler candidates, out of thousands.

    As more and more students of this matter are realizing, anyway,
    planets aren’t the action for prospective interstellar settlers,
    but instead the Grand Prize is a healthy population of ASTEROIDS,
    which can be immediately mined,
    unlike planets, so afflicted with a gravity well.

    Planets with an atmosphere
    prevent the use of
    solar-powered mass-catapults,
    such as we should have had on the Moon by now.

    The smaller the body the easier it is for settlers to exploit.

  • ljk August 26, 2011, 22:35

    Regarding potential life forms on a neutron star, check out Robert Forward’s SF novels Dragon’s Egg and Starquake. Though for my taste, the Cheela are a bit too human-acting in behavior than creatures which might actually exist under such conditions. But hey, I could be wrong here, too.

  • ljk August 26, 2011, 22:37

    And speaking of cosmic diamonds, is it still accepted that Jupiter and maybe the other gas giants have cores made of solid diamond the size of Earth?

    In Arthur C. Clarke’s SF novel 2061, a piece of that core the size of a mountain was found smashed into Europa after the Monolith ETI turned Jupiter into a sun.

  • Adam August 27, 2011, 2:42

    Contra Interstellar Bill, but I am pretty sure every planet mentioned has featured in SF, even if astronomy has lagged behind. The Black Planet, for example, would easily be Hal Clement’s Tenebra, which sucked in all incident light to keep its atmospheric ocean above the critical point. Interstellar planets have featured in multiple stories and were speculated about before the 1990s. Hot Jupiters… As someone has noted, Carl Sagan’s “Cosmos” featured a few in his ACCRETE simulations of planet formation. Diamond planets also appear, though maybe not diamond stars – though crystallized white dwarfs have been around for some time in astronomy. But exoplanets have definitely violated our assumption of mediocrity about the Solar System.

  • andy August 27, 2011, 7:53

    If Carl Sagan’s vaunted ‘Copernican Principle’ had the slightest validity, we would by now have found numerous Earth-type planets and even more nice, stable solar systems. There would have been a significant number of systems with TWO habitable planets.

    Interstellar Bill either doesn’t know or chooses to ignore that the ability to detect analogues of solar system planets is only just starting to become available. He is confusing the limitations and biases of detection methods with how things are in reality. And the solar systems we have found so far are indeed stable, I guess he is confusing orbital eccentricity and stability.

  • bigdan201 August 27, 2011, 10:58

    A planet that’s a gigantic diamond… amazing. I vote in favor of Lucy.

    Interstellar Bill either doesn’t know or chooses to ignore that the ability to detect analogues of solar system planets is only just starting to become available. He is confusing the limitations and biases of detection methods with how things are in reality. And the solar systems we have found so far are indeed stable, I guess he is confusing orbital eccentricity and stability.

    Indeed. Observational limitations skew the results towards planets that are easier to find (pulsar planets, hot jupiters, etc.). It is really exciting to see such great quantity and variety in exoplanets. Considering the super-earths we’ve found, I believe it will only be a matter of time before we find more earth-like terrestrial planets.

  • Eniac August 27, 2011, 12:52

    Oxygen is more common and dense than carbon. Would a crystallized stellar remnant that lost light elements then not be made up of dry ice and oxygen, rather than diamond?

    Come to think of it, a white dwarf is made from degenerate matter, so this “planet” would have had to revert back to regular matter somehow. I do not see any of this explained here or in the paper, where it talks about carbon in terms like “heavy elements such as carbon” and “possibly carbon-rich”, none of which would support the conclusion that this thing is made of diamond.

    Looks like we have here another one of these flights of fancy which morph out of much less “interesting” scientific findings through the sensationalization machinery of the popular press.

    Another question: What happened to the silicon? It would have to be gone missing, or else we would have just a plain old boring rocky planet, made from silicates or silicon carbide, depending on the relative abundances of carbon and oxygen.

    Not all is lost, though. If oxygen predominates the combined carbon, silicon, metals and remaining hydrogen, there might even be a non-biological nitrogen/oxygen atmosphere on top of a rocky planet, here. Perhaps distributed around the orbit in a ring, as Rob Henry proposes, with integral trees and all….

  • Gregory Benford August 27, 2011, 13:58

    Two decades ago I published a story, AS BIG AS THE RITZ, with a diamond world formed just this way. There were earlier astrophysics on how such a structure could evolve–yes, in a supernova/pulsar event. Good to see they actually exist!

  • andy August 27, 2011, 14:16

    Personally I don’t regard the companion of PSR J1719-1438 as a bona-fide planet. Makes more sense to regard it as an unusual type of stellar remnant (I guess it counts as an extremely undermassive white dwarf), the product of binary star evolution. This system tells us more about stellar binaries than it does about planets.

    This contrasts PSR B1257+12 which does at least appear to be the product of planet formation from a disc, albeit a disc with an unusual formation history. Incidentally regarding the fourth companion of PSR B1257+12, current view seems to be that the detection was an artifact: from this paper:

    There have been reports in the past (Wolszczan et al. 2000b) of additional timing residuals in the B1257+12 data that might be indicative of the presence of additional small planets at larger radii. However, subsequent observations suggest these are due to effects related to the propagation of radio waves through the interstellar plasma, and not gravitational in origin (Alex Wolszczan, private communication).

  • Dale Jacobs August 27, 2011, 15:52

    I have often wondered after our understanding of how the Earth’s core was formed. Earth’s outer core is thought to be composed mainly of a molten iron and nickel alloy with an inner core of ‘solid’ FeNi . This composition is assumed and based upon calculations of its density and upon the fact that many meteorites (which are thought to be portions of the interior of a planetary body) are iron-nickel alloys. Whereas the crust, through convective currents from below contains some few percentages of even heavier elements such as lead, gold and uranium, which appear to be extremely rare in our part of the galaxy. All of these elements are thought to have been created in supernova at extreme density and temperature ranges in the 2-5 billion degree K range.

    It seems to follow that there is a remote possibility the Earth itself may be the remnant core of a companion star to Sol which went supernova several billions of years ago? Several factors seem to correlate with this assumption including Earth and Sol’s common elemental composition, meteoric composition, the presence of our gas giants (Being a fraction of the ‘atmosphere’ of an exploded progenitor star) and the relative stability of Sol which would have been enriched and stabilized by the absorption of matter from that primordial explosion.

    If this wild assumption holds any truth to it at all, then another consideration might be the possibility that the CMB is evidence of an expanding shock front from such an explosion?

    All of this extrapolated from the statement above: “…a planet that may itself be the remains of a massive star. “

  • jkittle August 28, 2011, 1:20

    Interstellar Bill. I am with you- asteroids and icy dwarf planets will rule our future for a long while. mars is interesting and if they can solve the problem of landing 10 ton loads on the surface ( currently not at all practical with rockets of parachutes,)
    This diamond planet is a bit of a side show- See the amazing and distant freak of nature! I love it!

  • Phil August 28, 2011, 2:31

    I agree with Andy

    If we are going to be clear about the difference between planets and stars at their birth (even if their masses overlap) then we should be clear about the difference at their death. This is a very weird binary – a new and fascinating critter in a zoo that’s getting fuller by the week!


  • Adam August 28, 2011, 6:11

    High density physics is difficult to do, but there are a few things we’re pretty sure about. Supernovae come in two varieties, unless the star involved is super-massive. One variety, the Type Ia, are thermonuclear – the rapid fusion of carbon and oxygen – and involve the total destruction of the star involved. Type II supernovae are powered by gravitational energy – the irrevocable collapse of a star’s iron/nickel core into much denser neutronium. The outer layers are thrown off with sufficient violence to form immense amounts of heavier elements, mostly iron & nickel, but they’re dispersed at a significant fraction of the speed of light. So while Earth’s core has been forged in the violence of supernova, there’s no way it’s the former core of an exploded star.

    As for ljk’s question about “diamond cores” in the gas giants, the short answer is probably not. The more exotic possibility, because there’s a lot of carbon in Uranus and Neptune, is the formation of an ocean of liquid diamond, with chunks floating in it. Definitely maybe. Uranus also seems to have a strongly stratified interior, which is preventing heat loss, which leads one to speculate there’s a diamond shell around its hot core.

  • andy August 28, 2011, 6:42

    It seems to follow that there is a remote possibility the Earth itself may be the remnant core of a companion star to Sol which went supernova several billions of years ago?

    Unfortunately you’ve then got to explain the rest of the planetary system and getting everything into stable orbits. Also several other objects also have differentiated to form iron cores: Mercury, Venus, the Moon, Mars, the asteroid 4 Vesta, Jupiter’s moons Io, Europa and Ganymede (but apparently not Callisto) and probably several other objects. Your hypothesis would require a primordial system that looks nothing like any kind of multi-star system that has been observed, be wildly unstable, and have to have suffered multiple supernovae each of which would have the potential to unbind the entire system (due to mass loss), and then magically end up with everything in nice stable low-eccentricity orbits.

    The alternative, where core formation is a natural and expected process in a planet that is sufficiently hot to be molten explains the observations well and does not cause nearly as many severe problems as your supernova remnant idea.

  • Eniac August 28, 2011, 12:05

    Anyone have an idea how we know this star/planet is supposed to be made from just carbon, and not oxygen and silicon and other elements as well? Does the Alpha Process (http://en.wikipedia.org/wiki/Alpha_process) not apply? Why?

  • andy August 28, 2011, 14:45

    Eniac, as I understand it the “planet” is theorised to be the core of a carbon-oxygen white dwarf star, so presumably there would be quite a bit of oxygen in there, though this would probably depend on how much of these the progenitor star managed to make. Certainly studies of the cooling of white dwarf stars show that the core of the white dwarf gets enriched in oxygen (which is heavier and crystallises at higher temperatures) with more of the carbon towards the outer part of the core. Even the fabled “diamond star” BPM 37093 is best fit with an oxygen core model. As for silicon that depends on whether the progenitor got to making significant quantities of it. I doubt this thing would be pure carbon…

  • Mike August 28, 2011, 15:22

    I’ve reconsidered my opinion. It is after all a stellar remnant as it was once a star. Why start calling it a planet? But we could still call it Lucy. Unless it’s really an oxygen mini white-dwarf stellar remnant then we can call it ………… Rusty?

  • Dale Jacobs August 28, 2011, 16:05

    I would like to withdraw my above statement… to many late nights at the eyepiece catching up with me?

  • Eniac August 28, 2011, 16:32

    Here is the information I was looking for:


    First, it appears that the crystallisation of white dwarfs does not revert the matter back from the degenerate state, meaning that the material would be substantially different from diamond, many orders of magnitude denser, for one. To call it diamond is, as I suspected, a flight of fancy.

    Second, regrettably, the name Lucy seems to have already been taken by BPM 37093 in 2004: http://news.bbc.co.uk/2/hi/science/nature/3492919.stm

  • Eniac August 28, 2011, 17:03

    I almost forgot: Thanks, Andy, for pointing me to the crystallisation model and the 2004 Lucy. This is exciting stuff, diamond or not…

  • Rob Henry August 28, 2011, 21:16

    Eniac, I put it to you that the maximum excitement from such matter is not the liquid or crystal state, but the properties of the interface between. Note how (other than bone or cartilage) we seem entirely built from liquids (albeit some just fluid in two dimensions) that have taken on solid properties. I am wondering if anything complex can occur at the interface as in Robert Forward’s Dragon’s Egg.

    For that matter has anyone ever done a follow-up peer reviewed study over Forward’s complex-nuclear-chemistry speculation: or are such situations just too hard, and provide too much potential for embarrassment.

  • Adam August 29, 2011, 8:26

    Hi Rob Henry,
    Forward’s speculations aren’t unreasonable and nuclear chemistry is a reasonably lively area of research, but also computing what nucleii do in the conditions of even just the crust of a neutron star are very, very tricky. Maybe Forward was right, or at least making good guesses ;-)

  • Alex Tolley August 29, 2011, 13:32

    At this point, isn’t the concept just speculation? I’d like to see some more direct evidence that the companion is indeed primarily carbon in the core, let alone diamond.

    I also note that crystal structures denser than diamond are possible, so perhaps the companion is more like them, than diamond?


  • ljk August 29, 2011, 14:52

    Has anyone considered the possibility that PSR J1719−1438a could actually be made of… zirconium?!

  • andy August 30, 2011, 13:31

    Has anyone considered the possibility that PSR J1719−1438a could actually be made of… zirconium?!

    Formation mechanism please ;-)

  • ljk August 30, 2011, 15:35

    From S Class stars and as a by-product of certain alien mining efforts.

  • andy August 31, 2011, 16:14

    From S Class stars and as a by-product of certain alien mining efforts.

    I wonder if anyone’s considered it might be made of pork pie from certain alien farming efforts?

  • Eniac August 31, 2011, 21:37

    I also note that crystal structures denser than diamond are possible, so perhaps the companion is more like them, than diamond?

    The degenerate matter in a white dwarf is ~1,000,000 times denser than normal matter, and therefore quite unlike diamond or any other normal phase of carbon (or other elements).