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vonmazur
2005-Feb-15, 05:46 PM
Recently it was in the media, that some astronomers in the US had found some small Pluto sized planets orbiting a star that was more than 100 LY distant. I was wondering, since the star is the neutron remnant of a gas giant, how did any planet survive to still be orbiting the remains of a nova???

Dale in Ala

TravisM
2005-Feb-15, 07:05 PM
Current theories there involve the planets forming from the aftermath.

Maddad
2005-Feb-17, 05:09 AM
A Pluto sized-object at 100 light-years? It is only in the last month that I heard of the first Earth sized-object ever seen, and we're not sure we actually saw it. It was also much closer than 100 light-years away, and pluto is much smaller than Earth.

Some reporter's got his information scrambled.

The Bad Astronomer
2005-Feb-17, 05:55 AM
Nope, it's correct (http://www.universetoday.com/am/publish/smallest_extrasolar_planet.html).

It's orbiting a pulsar. The pulsar blinks at an extremely well-known rate. As a planet orbits, the arrival time of the pulses changes because the planet is tugging on the pulsar. These changes in the arrival time can be measured to figure out the orbit and mass of the planet (well, the mass isn't as well known, but the orbit is).

The very first extrasolar planets were discovered this way. A lot of people forget that.

Maddad
2005-Feb-17, 06:57 AM
Son of a gun! How about them apples? Wow!

the_shaggy_one
2005-Feb-17, 08:43 AM
I want to know why we havn't found any other pulsars with exoplanets besides PSR B1257+12 and the system containing Methuselah (http://en.wikipedia.org/wiki/PSR_B1620-26c).

Kullat Nunu
2005-Feb-17, 09:02 AM
It's orbiting a pulsar. The pulsar blinks at an extremely well-known rate. As a planet orbits, the arrival time of the pulses changes because the planet is tugging on the pulsar. These changes in the arrival time can be measured to figure out the orbit and mass of the planet (well, the mass isn't as well known, but the orbit is).

Pulsar timing is so accurate that mutual interactions between the two Earth-sized planets can be measured. That proved beyond doubt that these planets are real.

Kullat Nunu
2005-Feb-17, 09:19 AM
I want to know why we havn't found any other pulsars with exoplanets besides PSR B1257+12 and the system containing Methuselah (http://en.wikipedia.org/wiki/PSR_B1620-26c).

It may be that planets around pulsars are rare and their formation need some unusual event to happen.

Usually young pulsars rotate a few tens of times per second and their rotation slows down over time. However, PSR1257+12 is an old pulsar (billion years old) and is also a so-called millisecond pulsar that rotates abut 160 times per second. So something must have speed it up. It is speculated that it had a companion star that was completely destroyed by the pulsar (there are evidence (http://chandra.harvard.edu/photo/2003/b1957/) of such ongoing events). The planets may have been formed from the leftover disk.

PSR B1620-26 c (or "Metuselah") isn't likely a true pulsar planet, but a planet of a now dead sunlike star that the pulsar captured. That system is located in crowded globular cluster M4 so such star-capturing events are not very unlikely there.

AstroSmurf
2005-Feb-17, 10:42 AM
This is, like, so cool.

Erm, sorry about that. 8-[

vonmazur
2005-Feb-17, 04:32 PM
Guys; Thanks for the info, but I am still mystified by the existance of a planet circling a neutron star....

Dale in Ala

Jpax2003
2005-Feb-17, 05:18 PM
Of course now that the planet is discovered we can get to the exciting business of discussing whether it should be called a planet or not, just like Pluto.

Kullat Nunu
2005-Feb-17, 05:40 PM
I am still mystified by the existance of a planet circling a neutron star....

You're not only one...


Of course now that the planet is discovered we can get to the exciting business of discussing whether it should be called a planet or not, just like Pluto.

PSR1257+12 d is way too little for a planet, that's sure. But we can also argue what are the largest objects that can be called planets. For example, second planet of star HD 38529 has a minimum mass of 12.70 Jupiters. It was large enough to support deuterium fusion in its youth, and so qualify as a small brown dwarf. But if it formed like smaller planets it would be unfair not to call it a planet.