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Oldest Planet Ever Discovered
crymeph0 writes "NASA has found the oldest known planet in a globular star cluster in the constellation Scorpius. At 13.7 billion years old, it's just slighly (~1 billion years) younger than the universe itself. Get more info from HubbleSite"
Yup. Here's info from Hubblesite: The story of this planet's discovery began in 1988, when the pulsar, called PSR B1620-26, was discovered in M4. It is a neutron star spinning just under 100 times per second and emitting regular radio pulses like a lighthouse beam. The white dwarf was quickly found through its effect on the clock-like pulsar, as the two stars orbited each other twice per year. Sometime later, astronomers noticed further irregularities in the pulsar that implied that a third object was orbiting the others. This new object was suspected to be a planet, but it could also be a brown dwarf or a low-mass star. Debate over its true identity continued through the 1990s.
Sort of... The planet is in orbit around a binary consisting of a pulsar and a white dwarf. Previously, the pulsar had been observed and small variations in the arrival times of the pulses allowed them to detect the white dwarf companion. Further analysis of the pulsar arrival times allowed them to infer the existance of another distant companion, but there was still considerable uncertainty in the mass and orbit, so it wasn't clear if it was a planet or brown dwarf. These new observations pin down the mass of the white dwarf, which, when combined with several additional years of pulsar timing data, demonstrate that the mass is about 2.5 Jupiter masses.
But, the really interesting part of this paper is that since they now have directly observed the white dwarf around the pulsar, they can measure its colors and infer it's age. Previously, there were two leading theories... 1. That there was a pre-existing pulsar-white dwarf binary and then the planet was captured from it's orbit around a star which passed by the pulsary-white dwarf binary. -or- 2. There was a pulsar-star binary which interacted with a star-planet binary, kicked out the original star, replacing the old stellar companion with the new star, and leaving the planet in a wide orbit. The new star evolved, expanded, transfered mass onto the pulsar, spun up it's rotational speed, became a white dwarf, and circularized it's orbit around the pulsar. The planet stuck around in a wider orbit and perturbed the inner binary slightly, imparting a small eccentricty to the pulsar-white dwarf binary.
Since we now know the white dwarf is young, scenario 2 is vastly more likely, and so we now better understand the formation mechanism for this system. That's the real news behind this discovery.
BTW- The original paper is avaliable in today's issue of Science and I think it should be readable for someone with one college astronomy class.
Ah, but if our solar system is anything like a normal solar system and/or the computer models are true, then systems with large, detectable planets probably have smaller planet as well. Some of them might even be similar to Earth in size and composistion.
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Crudely Drawn Games
Yes, this is another interesting aspect of the story. We now have a much firmer constraint on the planet's mass, so if you define planets and brown dwarfs by their masses, then we are much more confident that it is a planet, and not a brown dwarf. However, we still don't know how it formed. Traditionally, brown dwarfs are assumed to form by direct collapse, while planets are assumed to form first by accreting a rocky core. Of course, we don't really know how this "planet" formed. Alan Boss advocates that it may have formed via direct collapse, like a brown dwarf, in which case the low metal abundance probably isn't so important. However, many scientists think that the accretion of a core first is more likely. Since we know that this planet exists and almost certainly formed in a low metallicity environment, that might be difficult in this case. I suspect someone will now attempt to simulate accretion of a planetary core in a low metallicity disk. I look forward to reading about their results.
It is odd, but not completely unexpected.
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The most accurate estimation of the age of the universe has been recently carried out by the WMAP mission, which measured the cosmic microwave background with 35 times the resolution of the previous COBE mission. The universe is 13.7 billion years old, plus or minus 200 million years.
Second, there are several projects planned, like the 'Darwin' project of the European Space Agency (ESA) that will specifically target earth-like planets. Here is a short description of Darwin, and links to some other projects.
For those who don't know what an H-R (Hertzsprung-Russel) diagram is, it's a diagram plotting all the stars in a graph with the following axes: Temperature (which can be measured accurately by looking at the spectrum of the star), and (absolute) Luminosity.
The thing to realise for the non-initiated here is that stars move around the H-R diagram throughout their life-time, as they form, expand into red dwarfs, blow away their outer shells, shrink into white dwarfs, etc. Through all this their temperature varies and their luminosity (which is largely dependent on their size, which changes vastly between, say, a star like the sun and the same star 5 billion years later when it's turned into a red giant) varies too.
However the vast majority of the stars in a cluster of average age will be stuck on a line which represents what is called the "main sequence", which is what our sun is on. Where they are on the line depends on their starting mass. Stars stay on the main sequence longer if they are lighter (heavy stars have much shorter lives), so there is a "turn-off" point on the main sequence line (a point where the stars move off the main sequence into the red giant phase) which can be used to evaluate the age of the cluster, assuming all the stars formed at roughly the same time.
Daniel
Carpe Diem
The planet is in a binary system with a neutron star and a white dwarf. The neutron star has already exploded as a supernova (neutron stars are the remnants of supernova explosions), and the white dwarf will never explode as supernova.
Yeah, 100 times a second, a normal star would fly apart, pulsars are not normal stars though and can withstand that spin due to how they are made. (100/s is actually pretty slow, 1K/s and 10K/s are also out there.)
Pulsars are nutron stars (collapsed due to gravity to the point of overcoming the repulsive force between atoms, so the nucleus of the atoms are smashed together, extremely high density matter just short of a black hole in density) where the angular velocity of the entire system is packed into a tiny space (meters or a few kilometers across).
Since it still has a magnetic field too, there is a "beam" of photons that get channeled out away at the poles, sorta like a flashlight spun on a string.
If earth is in the beam, we see a "pulse" of light energy coming from the star. (There's a proably a bunch we do not see as they do not point at us at any time during the spin.)
Counting the pulses tells you how fast the star is spinning and to a certain extent it's age (as the pulse slows down over astronomical time).
Since the spin has a lot of angular momentum (A LOT) it is extremely regular, and serves as a nice clock to use against stuff going on around the pulsar and between us and it. (Think atomic clock to synch GPS with, same concept.)
Or something like that.
Not necessarily -- or at least not for that reason. Remember that this is about as old as a planet can be, as it was formed when the universe was still quite young.
For a planet to form, there must already have been stars going supernova to create the materials the planet forms for. And this star material must also gather in large enough concentrations close to a gravity well (i.e. a star or another planet).
Finally, the gravity well it revolves around must be extremely long-lived for it to still exist -- alternatively, it must be at the "other side" of the universe, where we see it as it existed back then, with the probability that it no longer exists when we see it.
Yes, I believe we will find more old planets, but not primarily because of improvements in technology, but because the universe is frigging huge, with zillions of possible old planets.
Not MUCH older than this one, though.
Regards,
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*Art