One of the popular astronomy facts that gets passed around every so often is how small our Sun is compared to other stars. The Sun appears large to us, but it’s tiny compared to giant stars like Betelgeuse. While this is true, it isn’t the best metric for comparing stars. While Betelgeuse has a diameter 1,000 times that of the Sun, it only has 10 – 20 times the mass. Betelgeuse is much larger than our Sun, but also much less dense.
Kissing Cousins
In the constellation of Camelopardalis (also known as the Giraffe) is a faint star known as MY Cam. It appears faint because it is about 13,000 light years away, but its spectrum showed that it was actually a blue supergiant. Then recently, detailed measurements indicated that it was a spectroscopic binary consisting of two blue supergiants. Now a new paper in Astronomy & Astrophysics has revealed that the two stars orbit very, very closely.
All Alone in the Night
Although we think of deep space as being dark, that isn’t entirely true. The universe is filled with a background glow of radiation. The most famous is the cosmic microwave background, which is the remnant glow of the big bang. There is also the x-ray background, caused by things like active galactic nuclei, the radio background. This week new research on the infrared background has been published in Science, and the results are somewhat surprising.
Holding It Together
In the center of our Milky Way galaxy is a supermassive black hole. We can’t see this black hole directly because there is too much dust in the direction of galactic center, but radio waves can penetrate that dust, so we can observe the radio signals of hot stars and gas near galactic center. We’ve been observing these signals over several years, and we’ve noticed how the stars near galactic center orbit the region very quickly. From their orbital motion and a simple use of Kepler’s laws we can get a pretty good idea of the mass of the black hole. It turns out to be about 4 million solar masses. While this is a huge black hole, most of the stars orbiting it aren’t too terribly close. So for the time being they aren’t at risk of being ripped apart by the intense forces near the black hole. But there was one object recently that did make a very close approach.
Chemodynamics
Much of the modeling of astrophysical systems focuses on dynamical behavior. That is, how stars, planets and interstellar clouds move under the forces of gravity. While such dynamical modelling can prove useful for studying the motion of galaxies, they are not quite as good at modeling the evolution of galaxies. That’s because galaxies evolve over time not only due to the motion of stars within them, but they also evolve chemically as old stars die and new stars form. The chemical makeup of new stars depends where and when they form.
Older Than the Universe
The star HD 140283 is a subgiant star with an estimated age of 14.46 billion years. That might raise an eyebrow or two for those of you who remember that the age of the universe is estimated as 13.77 billion years. It would seem that this particular star, sometimes referred to as the Methuselah star is older than the universe.
Black Hole Sun
We know that supermassive black holes exist in the center of most galaxies, and they can become quite massive (upwards of billions of solar masses). What we aren’t sure about is just how they come to be.
Star Seed
One of the big mysteries in cosmology is how supermassive black holes formed in the centers of galaxies. Did they form directly from large concentrations of matter and dark matter, or did they form when early stars collided and accreted into massive black holes? Another idea is that they may have formed from the collapse of supermassive stars. In this idea stars with masses of 10,000 Suns or more could have lived short, violent lives before their core collapsed into a massive black hole. It’s an interesting idea, but new research shows that such supermassive stars might have a different fate.
Take It to the Limit
Yesterday I mentioned that hypernovae (super-supernovae) are the result of the explosion of a star that’s about as massive as a star can be (about 150-200 solar masses). But how exactly do we know that this is an upper limit?