Astronomers: ‘death star’ has devoured 15 Earth sized worlds

From PRINCETON UNIVERSITY and the “That’s no moon…” department:

Devourer of planets? Princeton researchers dub star ‘Kronos’

Sun-like star Kronos shows signs of having ingested 15 Earth masses worth of rocky planets, prompting Princeton astronomers to name it after the Titan who ate his children.

In mythology, the Titan Kronos devoured his children, including Poseidon (better known as the planet Neptune), Hades (Pluto) and three daughters.

So when a group of Princeton astronomers discovered twin stars, one of which showed signs of having ingested a dozen or more rocky planets, they named them after Kronos and his lesser-known brother Krios. Their official designations are HD 240430 and HD 240429, and they are both about 350 light years from Earth.

Sun-like star Kronos shows signs of having ingested 15 Earth masses worth of rocky planets, prompting Princeton astronomers to nickname it for the Titan who ate his young. This artist’s rendering of the diverse rocky planets in our galaxy hints at what Kronos’s planets might have looked like before the star enveloped them. CREDIT NASA/JPL-Caltech/R. Hurt (SSC-Caltech)

The keys to the discovery were first confirming that the widely separated pair are in fact a binary pair, and secondly observing Kronos’ strikingly unusual chemical abundance pattern, explained Semyeong Oh, a graduate student in astrophysical sciences who is lead author on a new paper describing Kronos and Krios. Oh works with David Spergel, the Charles A. Young Professor of Astronomy on the Class of 1897 Foundation and director of the Flatiron Institute’s Center for Computational Astrophysics.

Other co-moving star pairs have had different chemistries, Oh explained, but none as dramatic as Kronos and Krios.

Most stars that are as metal-rich as Kronos “have all the other elements enhanced at a similar level,” she said, “whereas Kronos has volatile elements suppressed, which makes it really weird in the general context of stellar abundance patterns.”

In other words, Kronos had an unusually high level of rock-forming minerals, including magnesium, aluminum, silicon, iron, chromium and yttrium, without an equally high level of volatile compounds — those that are most often found in gas form, like oxygen, carbon, nitrogen and potassium.

Stars HD 240430 and HD 240429, better known as Kronos and Krios, as they appear in the Space Telescope Science Institute’s Digitized Sky Survey. Though these binary stars formed together, their chemical abundances are very different, leading researchers to conclude that Kronos had absorbed 15 Earth masses worth of rocky planets. CREDIT NASA/JPL-Caltech/R. Hurt (SSC-Caltech)

Kronos is already outside the galactic norm, said Oh, and in addition, “because it has a stellar companion to compare it to, it makes the case a little stronger.”

Kronos and Krios are far enough apart that some astronomers have questioned whether the two were in fact a binary pair. Both are about 4 billion years old, and like our own, slightly older sun, both are yellow G-type stars. They orbit each other infrequently, on the order of every 10,000 years or so. An earlier researcher, Jean-Louis Halbwachs of the Observatoire Astronomique of Strasbourg, had identified them as co-moving — moving together — in his 1986 survey, but Oh independently identified them as co-moving based on two-dimensional astrometric information from the European Space Agency’s Gaia mission.

During a group research discussion at the Flatiron Institute, a colleague suggested pooling their data sets. John Brewer, a postdoctoral researcher from Yale University visiting at Columbia University, had been using data from the Keck Observatory on Mauna Kea, Hawaii, to calculate the spectrographic chemistries and radial velocities of stars.

“John suggested that maybe we should cross-match my co-moving catalogue with his chemical-abundance catalogue, because it’s interesting to ask whether they have the same compositions,” Oh said.

Binary stars should have matching radial velocities, but that information hadn’t been available in the Gaia dataset, so seeing their matching velocities in Brewer’s data supported the theory that Kronos and Krios, though two light years apart, were a binary set.

Then the researchers noticed the extreme chemical differences between them.

“I’m very easily excitable, so as soon as they had the same radial velocities and different chemistry, my mind already started racing,” said Adrian Price-Whelan, a Lyman Spitzer, Jr. Postdoctoral Fellow in Astrophysical Sciences and a co-author on the paper.

Oh took more convincing, both scientists recalled. “Semyeong is careful and was skeptical,” said Price-Whelan, so her first step was to double-check all the data. Once simple error had been ruled out, they began entertaining various theories. Maybe Kronos and Krios had accreted their planetary disks at different times during stellar formation. That one can’t be tested, said Price-Whelan, but it seems unlikely.

Maybe they only started moving together more recently, after trading partners with another pair of binary stars, a process known as binary exchange. Oh ruled that out with “a simple calculation,” she said. “She’s very modest,” Price-Whelan noted.

Oh’s skepticism was finally overcome when she plotted the chemical abundance pattern as a function of condensation temperature — the temperatures at which volatiles condense into solids. Condensation temperatures play a key role in planetary formation because rocky planets tend to form where it’s warm — closer to a star — while gas giants form more easily in the colder regions far from their star.

She immediately observed that all of the minerals that solidify below 1200 Kelvin were the ones Kronos was low in, while all the minerals that solidify at warmer temperatures were abundant.

“Other processes that change the abundance of elements generically throughout the galaxy don’t give you a trend like that,” said Price-Whelan. “They would selectively enhance certain elements, and it would appear random if you plotted it versus condensation temperatures. The fact that there’s a trend there hinted towards something related to planet formation rather than galactic chemical evolution.”

That was her “Aha!” moment, Oh said. “All of the elements that would make up a rocky planet are exactly the elements that are enhanced on Kronos, and the volatile elements are not enhanced, so that provides a strong argument for a planet engulfment scenario, instead of something else.”

Oh and her colleagues calculated that gaining this many rock-forming minerals without many volatiles would require engulfing roughly 15 Earth-mass planets.

Eating a gas giant wouldn’t give the same result, Price-Whelan explained. Jupiter, for example, has an inner rocky core that could easily have 15 Earth masses of rocky material, but “if you were to take Jupiter and throw it into a star, Jupiter also has this huge gaseous envelope, so you’d also enhance carbon, nitrogen — the volatiles that Semyeong mentioned,” he said. “To flip it around, you have to throw in a bunch of smaller planets.”

While no known star has 15 Earth-sized planets in orbit around it, the Kepler space telescope has detected many multi-planet systems, said Jessie Christiansen, an astronomer at the NASA Exoplanet Science Institute at the California Institute of Technology, who was not involved in the research. “I see no problem with there being more than 15 Earth masses of accretable material around a solar-type star.” She pointed to Kepler-11, which has more than 22 Earth masses of material in six planets with close orbits, or HD 219134, which has at least 15 Earth masses of material in its inner four planets.

“At the moment, we are still at the stage of piecing together different observations to determine how and when exoplanets form,” said Christiansen. “It’s difficult to directly observe planet formation around young stars — they are typically shrouded in dust, and the stars themselves are very active, which makes it hard to disentangle any signals from the planets. So we have to infer what we can from the limited information we have. If borne out, this new window onto the masses and compositions of the material in the early stages of planetary systems may provide crucial constraints for planet formation theories.”

The research also has implication for stellar formation models, noted Price-Whelan.

“One of the common assumptions — well-motivated, but it is an assumption — that’s pervasive through galactic astronomy right now is that stars are born with [chemical] abundances, and they then keep those abundances,” he said. “This is an indication that, at least in some cases, that is catastrophically false.”



60 thoughts on “Astronomers: ‘death star’ has devoured 15 Earth sized worlds

  1. At two light-years, there must not be much of a tidal effect between the stars, so accounting for the unstable orbits of planets must have some other cause.

    • Also, gas drag slowing their orbital motion & causing them to spiral inward is unlikely. Volatile-poor planets (e.g. Earth) are thought to form in orbit after intense stellar wind has driven most of the gas out of the inner system. In our solar system, planets out through Mars formed this way, whereas the outer gas giants formed while abundant volatiles were still present, and so accreted into the planets.

  2. “I’m very easily excitable, so as soon as they had the same radial velocities and different chemistry, my mind already started racing,”

    He needs some bromide.

    • Reply to Urederra…Or a valium to calm him down a bit. I would like to know how much this world staggering discovery has cost the working middle class of the world that actually produce the wealth that they waste. On the subject of colossal wastes of money in the sciency world, who’s heard the latest re the mystical “God particle?” Billions spent here as well for such a fleeting moment of sciency euphoria. And seeing how the scientific community have spent over two trillion dollars on global warming, I’m thinking they must already have the cure to cancer? Malaria? Power poverty? Hunger and thirst? A replacement for our dwindling antibiotic resources?….The common cold? They certainly haven’t cured stupidity. The various Govs. must have gigantic reserves of money set aside for emergencies? There must be simple economic solutions for world poverty? Or at least child poverty in developed nations? Homeless people on the streets in our own countries? The broken family down the street in our own home town who cant afford power, food, cloths or toys for their kids, let alone an aircon, a heater or a TV…Et freekin cet! I should expect to hear all about that cancer cure at any minute….surely?
      Or should we hire a common sense capable housewife to run everything? Because she would do an infinitely superior job. Would she feed her family and make sure they were not dying of disease before spending all her money and borrowing plenty more besides to peruse the imaginary Higgs Particle?
      As for the global warming lot…they are pure evil and they are bloody lucky I am not in Trumps position, see ‘The Spanish inquisition.”

      • Look Irritabel Bill,
        We have heard your rant all before. This is pure science in which we try and understand where and what we are. We do not know what the spin offs are. Your sort of rant would sound good when they were trying to find out the atomic theory. They are too small to be bothered with, they are much smaller than my Enoch!

      • “Irritable Bill October 12, 2017 at 4:35 pm
        Reply to Urederra”

        And what exactly do you propose?
        A massive bureaucracy of scientists only allowed to work on selected “good for humanity” causes? Similar to what Germany conducted up to and including WWII, Russia did for decades?

        All that ever creates is a massive bureaucracy where people are not allowed to innovate or think.

        The article describes actual scientists conducting research, recording observations and thinking. Nothing you are demanding offers that.

      • “On the subject of colossal wastes of money in the sciency world, who’s heard the latest re the mystical ‘God particle?'”

        As much as I am incline to agree with you, especially as your post concerns the global warming lot, Princeton is a private institution (quite fortunately).

      • I would like to know how much this world staggering discovery has cost the working middle class of the world that actually produce the wealth that they waste.

        A lot less than renewable energy has, anyway

      • I’ll reply to ATheoK because I agree essentially with the other rebuttals of my rant. I believe in pure science, I have an interest in these things myself which is why I am here reading this excellent blog…but there is a sane limit…I’m sure a sane person would agree we are massively past that if they cast their eye around, and the politicized nature of ‘mad science’ means that the size of the bureaucracy governing “science” today massively exceeds the entire budget of Soviet and Nazi war time budgets into science combined. And is seemingly beholden to no-one and brooks no dissent. And overall has no budget limit, especially if you mention global warming in your findings. How anyone could look at the IPCC and the UN and say that we shouldn’t seek to normalize the science budget is completely beyond of the realms of sanity.
        After the war, people had a perspective re. the importance of science and life in general, the importance of peace and community and living within ones means for the benefit of themselves and those to come…….If, ATheoK, you think that the direction we have taken as a society over the last few decades is superior to post war decades or advantageous to the citizens whose taxes you seem to think you have a right to without question…then you probably are a socialist yourself and if you don’t think tax funded science should be turned to the benefit of humanity because you want to think about the stars, then you are probably borderline evil also.
        Entities like Princeton (thanks Jonseingforozone, love the name) can fiddle around with nebulous theories and pure science, and dreamers can dream. I do plenty of it myself, and then I go to work and pay taxes…taxes that parasitic vermin such as yourself demand more of geometrically.
        eg. A guy in England I read about has had decades of tax payers money for observing a small bird I don’t remember which. He noted that the population has flourished over time and having larger nos. of healthier offspring as the living locally became easier as it had become more wooded, but wanted an extension to his grant for another decade because the white marking on its neck has become smaller and he thinks that it might be because of climate change….he was given his extension.
        Sorry about the long mail. Sometimes you have to respond or you are part of the problem. This about as brief as I could manage and still get the basic point across reasonably.

    • In other words, scientists are only to be allowed to research those subjects that Irritable Bill believes to be important.

      • We could agree on a general principle which states that whatever weirdness we might dream up, exists somewhere in the universe and in relative, if scattered abundance. Then, we could set about discovery and make efforts to explain what we found and try to make a buck off of it. (Sort of a vague look at science as we know it.)

  3. I wonder about the history of the stars’ mutual orbits. They may be moving gradually apart, after forming closer, but that just makes it more puzzling that one of the pair engulfed so much rocky matter, and the other so little.

    • It probably was due to the distribution of the matter as it was spun out between them. One of the two swept through the rocky debris while the other had a smooth ride.

  4. The sun and planets were all formed from the same mass of material. Our sun has little angular momentum compared with the planets. In that case it is reasonable to expect that heavy elements would congregate in the center of the sun and wouldn’t contribute to the solar spectrum. link

    Suppose that a star, for whatever reason, had a lot of angular momentum and heavy material were able to reach the surface. It would then appear in the spectrum. No planet gobbling would be necessary.

    • If a star has a significant angular momentum (from spin around its rotational axis), it will induce a shorter spin axis diameter and a longer equatorial diameter. The stellar shape is an oblate spheroid, rather than a uniform sphere. There are other measurable effects from stellar angular momentum as well.

      An extreme example of a ‘high angular momentum star’ is Regulus A. The equator of Regulus A has a measured rotational velocity of 317 ± 3 km/s and a rotation period of 15.9 hours. This is 86% of the velocity at which the star would break apart.

      • Agreed. I’m just trying to come up with a way to produce a certain spectrum that doesn’t involve devouring planets.

        It is very common for astronomical orthodoxy to be overturned by data from new and improved instruments.

        Cassini’s discovery of ocean worlds at Titan and Enceladus changed everything, shaking our views to the core about surprising places to search for potential life beyond Earth. link

        I have a feeling that the planet devouring theory isn’t the last word on the subject.

    • In such a scenario, all heavier elements would be concentrated in the sun. Not just the heavier elements with high boiling points.

  5. Yeaaaaaah. About this bullshit article.

    They simply wouldn’t know at this distance. 15 Earths wouldn’t even show up as a blip on the spectra.

  6. “has devoured 15 Earth sized worlds” ”

    the green agenda must feel it has a long way to go !!

    Only just getting started.

  7. Yet more cosmological fantasising based on assumptions of dubious worth. I expect that “Oh’s skepticism” was formed by the prospect of selling what amounted to a jar of pickled unicorn-shit, and it faded when she had just enough evidence to make the idea vaguely credible.

    On the bright side, if cosmology doesn’t work out as a career for these Princetonians, there is plenty of scope for this degree of scientific rigour in climatology.

  8. Curious I am about the use of the term ‘co-moving’ here.

    In the context of this study, does this mean that this binary pair orbits around a common center, like pair of skaters facing each other in a spin? E.g. Skater 1 (Center) Skater 2.

    Just trying to get the image of such movement in my head. Thanks for feedback.

    • Most stars (about 75%) are members of multiple star systems. Single stars, like out Sun, are rarer. For example, Polaris is a three star system. Our closest star system, Alpha Centauri, is also a three star system. The brightest star in the sky, Sirius, has a white dwarf companion. Some binary stars are so close that they spin around each other like a pair of skaters. Others are so far apart, that it is sometimes difficult to tell if they are orbiting each other.

      The current model for type Ia supernovae is a close binary pair where one companion is a white dwarf and the other is a red giant. The red giant companion feeds the white dwarf mass until it trips over its Chandrasekhar limit and explodes.


  9. “The keys to the discovery were first confirming that the widely separated pair are in fact a binary pair, and secondly observing Kronos’ strikingly unusual chemical abundance pattern…”

    The clincher, though was a SETI intercept of a bill from Chiron Sedation Dentistry for “full dental arch replacement, Kronos – result of eating too many rocky planets.”

  10. A star can be low in Carbon, Oxygen, Nitrogen if it formed from the remnants of a very large supernova.

    Basically, the Oxygen, Silicon, Carbon are consumed into the implosion inward toward the Fe Iron core (forming a black hole in this instance by way of being a very large supernova) and/or the Oxygen and Carbon get converted into more massive elements in the explosion outward half of a very large supernova – anything more massive than Fe Iron/Nickel is formed in the outward explosion of supernova – most of the time, the Carbon and Oxygen survive this explosion at a 50% or so rate but the very largest ones might convert the vast majority of these elements into heavier varieties. .

    One star forms from the left-overs of a cloud mostly made up of the remnants of the very large supernova and the other star forms from the general mix of dozens of different red giants and normal-sized supernovas. At some point, they end up 2 light years from each other and become a binary system.

    Shells just before supernova which are not to scale but are illustrative

    • Thanks Bill,

      this press release ( with the obligatory omission of any reference to the actual source it is supposed to be reporting on ) seems typically ignorant. Whether the paper is equally ignorant would be nice to find out.

      volatile compounds — those that are most often found in gas form, like oxygen, carbon, nitrogen and potassium.

      At the point where someone refers to chemical elements as “compounds” I stop taking anything they say on the subject as being accurate. Typical of “media studies” undergrads writing press releases on subjects of which they have NO knowledge whatsoever.

      co-moving — moving together

      Thanks for explaining that really obscure bit of jargon, we would never have worked it out on our own.

      Always useful having someone who knows nothing trying to be condescending.

      • Greg October 13, 2017 at 1:47 am
        this press release ( with the obligatory omission of any reference to the actual source it is supposed to be reporting on ) seems typically ignorant. Whether the paper is equally ignorant would be nice to find out.

        The original press release has a link to the paper, it has apparently been dropped in the cut and paste process.

  11. Astrophysicists can ascribe high level details about a loose-binary star system that’s 2 LY apart and 350 LY away from us, yet they can’t entertain the idea of a 9th large gas giant planet in our own solar system, AKA Nibiru?

    Forgive me—I’m no astrophysicist—but without testable data, “theories” can be pretty much whatever these people wanna pretend to be “true” without any dissention.

    • “… can’t entertain the idea of a 9th large gas giant planet in our own solar system”

      Well they are entertaining the idea. There are several papers on it. There are indications of something massive out there but its location is only very roughly indicated due to very short observational periods in relation to the orbit of the order of 10ka .

      If you insist on it being called Niburu you are linking it to all sorts of crazy shit that no one with half a brain is going to take seriously.

      It’s interesting that the demotion of Pluto means that anything they do find will be a new 9th planet and NOT the tenth : ie not planet X. Just a coincidence ?

      • Kicking Pluto out of the club means that they can say “we’ve discovered a new planet” with having to admit that planet X whose existence they have been ridiculing for years, actually exists. Clever move by Grasse-Tyson.

    • If there was a 9th gas giant, there would be evidence for it in the orbital perturbations of the other planets.

      Beyond that, they do have testable data. They have spectrographs of each star.

  12. This sounds a little too much like science fiction although is probably harmless at this point. I guess it doesn’t hurt to speculate about things with some scientific instruments and all, but I hope they don’t take themselves too seriously. Making statements like ‘devoured 15 earth like planets’ sort of sounds like alarmism to me. Hopefully these folks don’t start doing climate science here on earth.

    • … devoured 15 earth like planets …

      You won’t get published if you don’t say something interesting. You won’t get a job if you don’t publish. There’s no punishment for eventually being proven wrong. As a result, BS is fully baked into the system.

      There is an oversupply of scientists and the result is a lot of bad science as folks grasp at straws trying to come up with something they can publish. link

      It may also be affecting the quality of postdocs’ research, said McDowell, who cites a recent bioethics report that shows a significant number of scientists have considered changing research data to get published in the kind of journals that can help them land jobs.

      That, of course, is outright fraud. Could that happen in climate science … WELL DUH!

      • The climate scientists would be more accurate if they went to Kronos and observed and guessed from there.

  13. Given how far apart they are, two other possibilities present themselves.
    1) The cloud that formed them both was not uniform is it’s makeup, resulting in stars that were more different from each other than average.
    2) They weren’t formed from the same cloud and did not become a pair until well after they were formed.

  14. This nonsense passes for science, because of expensive equipment and models

    To interpret this as ingested planets is a laughable leap.

  15. How do we know stars don’t eject matter occasionally? We don’t, but of course, a few hundred years with telescopes and we think we understand the universe, mainly via mathematical constructions, oh the arrogance

    • Was thinking that, also. Thanks to you two “Marks”. Laughable indeed! These are scienists? Ok to think of scenarios but way too soon to be put forth as serious theories. More like ideas.

  16. The theory of planetary formation via disc accretion appears to have similarities to AGW. It looks like an invented theory with very little sound evidence to support it. More of a fanciful guess rather than a theory (Yes, yes, I know…Richard Feynman…”Guess”). Astrophysics is a great subject for guessing, theories and computer modelling. Lab experiments are rather costly and basic data gathering is not exactly a weekend trip to the site. I suspect a high percentage of current theories in this field will eventually turn out to be complete BS. Still interesting to read though, as was “Alice in Wonderland”.

  17. Rober Muller, in his book “Nemesis: the death star”, advanced the hypothesis of Alvarez et al. that the mechanism by which large comets hit the earth is the close passage a remote twin star of the sun, which they named “Nemesis”. The basic concept is that on close approach to the solar system every 26,000,000 years Nemesis caused enough gravitational effect on bodies on the outer edge of the system to send some of them on a collision course with the inner planets, taking approximately 4,000,000 IIRC, to reach the target.

    If this were true, then presumably our sun should also have collected a considerable amount of extra non-volatile elements in the course of the past 4 billion years…

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