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If you could approach closely enough (which, of course, you couldn’t), what would the surface of a neutron star look like?
Herman D’Hondt
Sydney, Australia
Neutron stars are formed when giant stars run out of fuel. Their internal pressure is no longer sufficient to fight gravity, and the resulting collapse and supernova explosion leaves a tiny core, with the same density as an atomic nucleus.
Typically they have a mass of about 1.5 times that of the sun, compressed into a 10 kilometre diameter ball. As they still have the angular momentum of the star, they rotate extremely rapidly; the fastest known does so 716 times per second. Over millions of years, their magnetism slows them down.
The slowest known neutron star rotates once every 54 minutes. At that speed or slower, you would be looking at the most perfect sphere in the universe. A faster rotating star will be an ellipsoid – a squashed sphere, somewhat like Earth.
The smoothest sphere ever created on Earth was made by the team of the Avogadro project. It was expected to be used for a new definition of the kilogram, but another method was selected. The sphere is made from a single crystal of silicon-28 with a diameter of 93.6 millimetres, accurate to 50 nanometres or 0.0000066 per cent. A neutron star would be roughly 1000 times smoother than this.
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To approach a neutron star, you’ll need a very good heat and radiation shield, and some strong thrusters on your spaceship
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Looking at a neutron star, it will probably appear as a very shiny ball. While neutrons themselves don’t reflect light, the star is probably covered in a thin layer of protons, which may look like a shiny metal coating.
Hilary Shaw
Newport, Shropshire, UK
In short, very smooth and very bright. A newly formed neutron star has a surface temperature in the millions of Kelvin, making it appear bluish-white, although most of its radiation is in the form of X-rays. Because of the intense gravity, the highest “mountains” that could exist on the surface would be less than 1 millimetre high, but they would take more energy than you could expend in a lifetime to climb. With a typical diameter of 20 km, this makes them one of the smoothest objects in the universe (after black holes).
Interestingly, their specific heat capacity is low, so an isolated neutron star might cool rather quickly, and within 1 million years of formation it could look white, then yellow-white. However, this is unlikely because it would also be converting its rotational energy to heat, and it could accrete enough interstellar hydrogen onto its surface to further collapse into a black hole.
So if you want to approach one, get a very good heat and radiation shield, and ensure you have strong thrusters on your spaceship to counter the intense gravity. Even that won’t save you, as the viciously strong magnetic field will turn the atoms of your spaceship, and you, into cigar shapes (aligned vertically to the star), and you and the spacecraft will become monatomic dust.
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