“Life Beyond Our Imagining?” — Exoplanets of Neutron Stars

Neutron Star Geminga

 

What would life be like on a planet orbiting a pulsar? Astronomers estimate that the Milky Way galaxy contains an estimated 1 billion neutron stars, of which about 200,000 are pulsars –neutron stars of only 10 to 30 kilometers in diameter with enormous magnetic fields, that accrete matter and regularly burst out large amounts of X-rays and other energetic particles. So far, 3000 pulsars have been studied and only 5 pulsar planets have been found. In 1992, the first exoplanets ever were discovered around pulsar PSR B1257+12.

Harvard astronomer Avi Loeb suggests that “it is reasonable to assume that planets might also exist around black holes, which, perhaps surprisingly to many people, have a much weaker impact on their environment than pulsars. It’s even possible that life may form on some of these planets, given that organisms on Earth have adapted to extreme conditions, including boiling heat, freezing cold, and acidic, highly salty and even radioactive environments.”

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On Earth, we know that the tardigrade, an eight-legged microscopic creature can exist for up to 30 years without food or water and endure temperature extremes up to 150 degrees Celsius– will exist until the Sun dies.

“They are as indestructible as it gets on Earth,” reported an Oxford University collaboration, “and is likely to survive all astrophysical calamities such as asteroid impact, supernova explosion or gamma ray bursts. “but it’s possible that there are other resilient species elsewhere in the universe. There is a real case for looking to Mars and other areas of our solar system. If tardigrades are Earth’s most resilient species, who knows what else is out there.”

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Inhabited planets, says Loeb, could survive near the supermassive black holes that lie at the cores of most galaxies. Our own galaxy, the Milky Way, harbors a black hole Sgr A* (Sgr stands for Sagittarius), with an innermost stable circular orbit that’s about the size of the orbit of Mercury.

In December of 2017, The Daily Galaxy reported that it is theoretically possible that habitable planets exist around pulsars. Such planets must have an enormous atmosphere that converts the deadly X-rays and high energy particles of the pulsar into heat. This was the conclusion of the paper by astronomers Alessandro Patruno (Leiden University and ASTRON) and Mihkel Kama (Leiden University and Cambridge University) who suggested that there could nonetheless be life in the vicinity of these stars.

It is the first time that astronomers have tried to calculate so-called habitable zones near neutron stars. The calculations show that the habitable zone around a neutron star can be as large as the distance from Earth to the Sun.

An important premise is that the planet must be a super-Earth with a mass between one and 10 times that of the Earth. A smaller planet will lose its atmosphere within a few thousand years. Furthermore, the atmosphere must be a million times as thick as that of the Earth. The conditions on the pulsar planet surface might resemble those of the deep sea.

The astronomers studied the pulsar PSR B1257+12 about 2300 light-years away in the constellation Virgo. They used the Chandra Space Telescope, which is specially made to observe X-rays. Three planets orbit the pulsar. Two of them are super-Earths with a mass of four to five times the Earth. The planets orbit close enough around the pulsar to warm up.

“According to our calculations, the temperature of the planets might be suitable for the presence of liquid water on their surface,” said Patruno. “Though we don’t know yet if the two super-Earths have the right, extremely dense atmosphere.”

Source: A. Patruno et al. Neutron star planets: Atmospheric processes and irradiation, Astronomy & Astrophysics (2017). DOI: 10.1051/0004-6361/201731102

Image at the top of the page shows the neutron star, Geminga taken with the EPIC instrument on board the XMM-Newton observatory. The bright tails, made of particles kicked out by Geminga’s strong magnetic field, trail the neutron star as it moves about in space. ESA, P. Caraveo

The Daily Galaxy, Avi Shporer, Research Scientist, MIT Kavli Institute for Astrophysics and Space Research via University of Cambridge and Scientific American, Avi was formerly a NASA Sagan Fellow at the Jet Propulsion Laboratory (JPL).

 

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