How do we know the shape of the Milky Way galaxy, when much of it is obscured by gas and dust?
A new analysis of astronomical data has found the Milky Way may be larger than we’ve thought.
From the light of our galaxy we can see not only what’s there, but the dynamics of how it’s changing.
At least one spiral arm of our home galaxy may extend much farther than we thought.
Earlier this year I wrote about a diffuse band of gamma rays coming from regions above and below the Milky Way. The regions spanned about 25,000 light years above and below the galactic plane, and are thought to have formed from an active period of our galaxy’s supermassive black hole about 2 million years ago. While we could determine the size of these regions from their x-ray and gamma ray emissions, it has been difficult to determine their motion. But yesterday at the American Astronomical Society Meeting, new results from the Hubble telescope are measuring the motion of these regions using an interesting trick.
The Sun orbits the center of the Milky way at a speed of about 230 km/s, taking about 250 million years to go around the galaxy once. It is a period of times sometimes referred to as a galactic year. But the Sun does not move in a simple circle or ellipse as the planets move around the Sun. This is due to the fact that the mass of the galaxy is not concentrated at a single point, but is instead spread across a plane with spiral arms and such. As a result, while the Sun orbits the galaxy it also moves up and down across the galactic plane. While the Sun is above the plane, the mass of the galaxy works to move it downward, and when below the plane the mass pulls it upward. As a result the Sun oscillates through the galaxy, crossing the galactic plane once every 30 million years or so.
While we’re quite familiar with our side of the Milky Way galaxy, the far side of our galaxy is still a bit of a mystery. The reason for this is that the center of the Milky Way is filled with gas, dust and stars, so it is very difficult to see the other side of our galaxy. The central region is so cluttered with material that it sometimes referred to as the Zone of Avoidance, since we have to exclude that region from observations beyond our galaxy.
The metallicity of a star is a measure of how much metal (elements other than hydrogen and helium) a star contains. New data on the amount of magnesium in stars suggests that stars our galaxy formed in the central region first, and only later at the outer regions.
By measuring the distribution of hydrogen in our galaxy, we know that our galaxy is a barred spiral.