Large Magellanic Cloud & Comet 252P/Linear

The wings of the Twin Jet Nebula are the remnants of a dying star at the nebula’s centre, flung off by jets of gas.  The nebula is 2,100 light-years from Earth, and a white dwarf star orbits the dying star.

Wispy remains of a supernova explosion hide a possible ‘survivor.’ Of all the varieties of exploding stars, the ones called Type Ia are perhaps the most intriguing. Their predictable brightness lets astronomers measure the expansion of the universe, which led to the discovery of dark energy. Yet the cause of these supernovae remains a mystery. Do they happen when two white dwarf stars collide? Or does a single white dwarf gorge on gases stolen from a companion star until bursting? If the second theory is true, the normal star should survive. Astronomers used the Hubble Space Telescope to search the gauzy remains of a Type Ia supernova in a neighboring galaxy called the Large Magellanic Cloud. They found a sun-like star that showed signs of being associated with the supernova. Further investigations will be needed to learn if this star is truly the culprit behind a white dwarf’s fiery demise.

 This supernova remnant is located 160,000 light-years from Earth. The actual supernova remnant is the irregular shaped dust cloud, at the upper center of the image. The gas in the lower half of the image and the dense concentration of stars in the lower left are the outskirts of a star cluster.

Image credit: NASA, ESA and H.-Y. Chu (Academia Sinica, Taipei)

White Dwarfs and Neutron Stars

What happens to a star after it dies depends entirely on the mass it contains. If the star has a low to medium mass (anything less than 8 solar masses) then at the end of its life it will transform into a white dwarf. If a star is massive (8-20 solar masses) then it will turn into a neutron star.

When a red giant starts to fuse helium to carbon and oxygen but lacks the mass to generate the core temperatures required to fuse carbon, an inert mass of carbon and oxygen will build up at the core. Towards the end of the stars nuclear fusion stage, it will shed its outer layers in the form of ionized gas forming a planetary nebula. The core that is left behind is the white dwarf typically about the size of earth. This is made up of electron degenerate matter which forms because the white dwarf lacks its previous ability to create an internal pressure meaning gravity squashes the mass much closer together. The reason this is happens is because under normal circumstances electrons with the same spin can’t occupy the same energy level, and there’s only two ways an electron can spin (this is known as the Pauli Exclusion Principle). In a normal gas this isn’t a problem because there aren’t enough electrons to fill the energy levels. In a “degenerate” gas however, all its energy levels filled. For a white dwarf to be forced smaller by gravity, it would have to make electrons go where they couldn’t go thus white dwarfs survive through quantum mechanical principles that prevent their collapse further. There are other unusual properties as well, white dwarfs with greater masses are actually smaller because gravity has to force the electrons closer together to maintain the outward pressure. However the limit to how much mass they can have is about 1.4 solar masses.

Neutron stars are incredibly dense (and one of my favourite things ever) with a typical one being about 20km and containing 1.4 solar masses. A teaspoon would weigh about a billion tonnes on a neutron star, that’s how dense they are. They are also composed entirely of neutrons as the force of gravity is so great that it has caused the electrons and protons to fuse into neutrons. The power from the resulting supernova that created the star causes it to spin up to 43,000 times a minute, gradually slowing over time. The neutron stars which are still spinning emit electromagnetic radiation that we can detect when it’s pointing towards earth (much like a lighthouse). These are known as pulsars. The magnetic axis of a pulsar is what determines the direction the beam will fire off in. However this is not necessarily the same as the rotational axis and this misalignment is what causes some to appear to pulse. There are currently three different types of pulsars that astronomers are aware of. The first is rotation powered pulsars which the radiation given off is caused by a slowing down of the rotation of the star. Accretion powered pulsars occur when the gravitational potential energy that falls onto the neutron star causes X-Ray’s that can be received from Earth. Finally there is magnetars where the radiation is caused by an extremely strong magnetic field losing energy.

Remnants from a star that exploded thousands of years ago created a celestial abstract portrait, as captured in this NASA Hubble Space Telescope image of the Pencil Nebula.

Credit: NASA and The Hubble Heritage Team (STScI/AURA)

Orionids Meteors Over Wulan Hada Volcano

Earth and Luna from the ISS

Remnants from a star that exploded thousands of years ago created a celestial abstract portrait, as captured in this NASA Hubble Space Telescope image of the Pencil Nebula.

Credit: NASA and The Hubble Heritage Team (STScI/AURA)