A family of stars

Stars don’t last forever and in this article we explored what might happen to our sun in a few billion years. This time we’re going to have a look at some recent observations and how they are leading us to better understand our own star. There are now significantly more powerful instruments available to gain a better understanding of the evolution of stars from when they are born to when they die like SN1054 and SN1987A. Of course, the star we know the most about is our own Sun and the cover image for this article, from NASA, shows it in all of its glory blasting out piles of radiation that keeps us warm. This time of the year the sun is of particular importance to us as we celebrate Christmas, New Year and any of the other events that roughly coincide with either the Winter Solstice or the Summer Solstice depending which Hemisphere you’re in.

We are understanding more and more about stars others than our own, for example Betelgeuse in Orion has long been a star that attracted a lot of attention. When it was imaged earlier in the year by the Atacama Large Millimetre/Submillimetre Array (ALMA) is attracted a lot of attention as being the most detailed image we have ever seen of star other than our own. Betelgeuse is massive, it is around 1400 times bigger than the Sun and one of the largest stars around. It is incredibly unstable with an asymmetric shape. As far as the life cycles of stars go, Betelgeuse doesn’t have long left, and may well have already exploded, just we may not know for a while as it’s 600 light years away. The star is around 8 million years old and because it’s burning through its fuel so quickly it is racing for the life cycle stage. When it does explode, it will go supernova and be an impressive sight and easily visible from Earth during the day. Below is the image from the European Space Observatory ALMA produced here.

Betelgeuse, ESO

ESO seems to produce some of the best images of other stars including the below one of an exo-planet orbiting a brown dwarf star about 230 light years away taken by the Very Large Telescope in Chile. Though not much surface detail is available from the image of the star it is an amazing image because it is one of the first that directly images an exo-planet. Brown Dwarfs are a very interesting family of stars. They are at the small end of star sizes with the smallest being just over 13.6 times the size of Jupiter, these stars are not big enough to start fusing hydrogen so don’t ignite like a normal star. Some higher mass Brown Dwarfs can sustain a fusion reaction for a few million years before radiating too much heat. The planet in orbit around the star depicted below is around 4 to 5 times the mass of Jupiter and orbits at twice the distance of Neptune from our Sun.

2M1207, ESO

The next image also from ESO is of the big red star in Scorpio’s called Antares. It’s a red supergiant and like, Betelgeuse, is in the late stages of its life. Antares probably started out life about 15 times the size of the sun and has lost about 3 solar masses in the last stage of its life. This loss of mass and the mechanism that causes it is an area of study that lead scientists to taking the below image using ESO’s Very Large Telescope Interferometer (VLTI) in Chile. With the data they collected they have been able to map the flow of gases in the atmosphere of the star and gain a better understanding of what is happening in the star.

What the scientists have been able to do is map the relative speed of the gases across the entire disk of the star and they found turbulent low density gas a lot further from the star than they anticipated. This led to the conclusion that this movement of gases could not be because of convection, there must be some other mechanism at play to cause this.

Antares, ESO

The above photos are fantastic but they have been surpassed by the below, which is the latest from ESO, which is an image of a giant star called π1 Gruis, in the constellation Grus. This star is quite fascinating as it’s a cool red giant about the same mass as our Sun but of an enormous size, about 350 times larger and a lot brighter. This star is really a snapshot of what our own star will look like in about 5 billion years when it has stopped burning hydrogen in the core and is struggling to hold onto its outer layers. Once again, scientists used ESO’s VLT to gather the data for the below image. What they found were a few very large cells of convective currents about 120,000,000 kms across, which is just a bit under the distance from our Sun to the Earth. When our star goes through a similar process it will see a ballooning of the outer layers as they continue to expand pushed out by the intense pressure from the core burning helium into oxygen and carbon, which outweighs the inwards pressure of gravity, collectively called hydrostatic equilibrium.

π1 Gruis, ESO

The new instruments that are available now to scientists are increasing our knowledge of star life cycles at a staggering rate. Only 20 years ago it was inconceivable to be able to see a detailed image of star’s surface to the fidelity of the above image. When the Extremely Large Telescope is added to ESO’s arsenal in a few years we’re in for even more startling treats with its 39m main mirror it will be a amazing window into the universe. The ELT is due to become operation by 2024.