Our Stellar Neighbourhood
Our part of the galaxy is a quiet spot. If the galaxy was a city we’d be in the suburbs, not the rural lifestyle blocks of the outer suburbs but the leafy wide streets that have the odd shopping centre. The hustle and bustle of the crowded galactic centre is a long way from the sleepy neighbourhood of where our Solar System hangs out. Despite the quite surrounds there are a number of hidden attractions including erupting red dwarfs, white dwarfs and multiple systems.
Of the nearest 100 star systems only 18 stars are visible to the naked eye, meaning the vast majority of our stellar neighbourhood is hidden from view.
This is because stars, despite their incredible size, are massive distances apart.
The distance covered within our own stellar neighbourhood of 100 star systems spans 50 light years or just under 500 trillion kilometres. The outer area of this local bubble of space has been subjected to electromagnetic emanations from our planet for the last 100 years. Aside from torturing our stellar neighbours to our tastes in television we have also been bathing this area of space in the radiation from our Sun.
Our Sun is in the middle of our local stellar neighbourhood, of course, but this does not mean it is necessarily gravitationally bound to any of the other stars. It does mean that our star can be readily seen by any observer that may be residing near any of the other stars but all the stars in our neighbourhood are not so easy to see.
Our star is not the biggest of the group, it is an averaged sized quiet star, all on it’s own. One of the things that we notice in our stellar neighbourhood is the number of multiple star systems. The closest stars to us is a group of three orbiting each other, Alpha Centauri A & B and Proxima Centauri. The first two, Alpha Centauri A & B, are very similar to our own Sun whereas Proxima Centauri is a tiny red dwarf and is actually the closest star to our Sun. It’s mass is only 11% of the Sun’s and we can’t see it with the naked eye as it’s only 11.05 in magnitude, Sirius is 550 times brighter and twice the distance.
Sirius is the next closest visible star, but within that distance is the tiny Wolf 359, Lalande 21185 and Barnard’s Star. All of these are red dwarfs.
Barnard’s Star is a favourite of astronomers as it’s the star with the highest proper motion of any of the stars in the night sky.
That means it’s the star that moves the fastest in relation to the position of the other stars, and it does move fast, at over 10 arcseconds per year.
The huge hot star Sirius has a surface temperature of nearly 10,000 degrees K and has a mass twice that of the Sun’s. It’s the brightest star in the night sky and is visible the world over. It’s the little companion of Sirius that is very interesting as Sirius is a system of two stars — one large bright one and one tiny stellar remnant of a star called a white dwarf. It’s mass is about that of the Sun but it’s crushed down to about the size of the Earth. The little stellar remnant still produces 25,000 degrees K which is all that is left of the core of a star long gone.
Heading to the other side of the Sun is another star similar to Sirius but a bit smaller and cooler and twice the distance, the beautiful Altair. This star is one of the stars that makes up the summer triangle of the Northern Hemisphere. What is amazing about this star is it’s rotational velocity at 210km/s. It rotates every ten hours and this causes a slight squashing of the star. Also at about 16 light years away is the magnitude 4 star Omicron 2 Eridani, also known as Keid. Keid is about 3/4 the mass of the Sun and has a number of interesting companions.
Keid is a very common type of star, the galaxy is full of them, far more abundant than stars like our Sun but it’s one of the few that you can see with the naked eye as these stars don’t put out a lot of luminosity so they are quite faint. This star system gets more interesting though because orbiting Keid is the most visible white dwarf of the night sky, GJ 166 B with a magnitude of 9.5, so you’ll need a good telescope to see it.
This white dwarf is about 1.5 times the size of the Earth and has a mass half as much as the Sun, you may recall that the white dwarf companion of Sirius was about the mass of the Sun yet the size of the Earth. That’s how they work, the higher the mass the smaller they are.
The story about Keid does not end there. The white dwarf is orbiting another star, a tiny red dwarf GJ 166 C or 40 Eridani C. This little star is 16% of the mass of the Sun and occasionally erupts with massive flares.
Though our neighbourhood is a quiet corner of the galaxy it doesn’t mean there’s nothing is happening here, as just a few light years away there’s a wealth of bizzare and amazing stellar objects to intrigue professional and amateur astronomers alike.
