Cosmicinsightz - Within The Cosmos

Milky Way - Spiral Galaxy

What caused this outburst of this star named V838 Mon? For reasons unknown, this star’s outer surface suddenly greatly expanded with the result that it became the brightest star in the entire Milky Way Galaxy in January 2002. Then, just as suddenly, it faded. A stellar flash like this had never been seen before – supernovas and novas expel matter out into space.

Although the V838 Mon flash appears to expel material into space, what is seen in the above GIF from the Hubble Space Telescope is actually an outwardly moving light echo of the bright flash.

In a light echo, light from the flash is reflected by successively more distant rings in the complex array of ambient interstellar dust that already surrounded the star. V838 Mon lies about 20,000 light years away toward the constellation of the unicorn (Monoceros), while the light echo above spans about six light years in diameter.

Credit: NASA, ESA

To discover more, visit: https://www.nasa.gov/multimedia/imagegallery/image_feature_2472.html

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.

This image shows what it might look like standing on the surface of a planet orbiting a brown dwarf star. An alien moon can also be seen in the sky. The brown dwarf gives off such feeble visible light it is difficult to see any of the landscape except for the reflection in the water.

credit: Jeff Bryant

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Stars and Dust in Corona Australis

Earth and Luna from the ISS

Large Magellanic Cloud & Comet 252P/Linear