Observing – astroengine.com

Yearly location of stars within 0.2 parsecs from Sagittarius A* orbiting the common, compact radio source (A. Ghez)

We are told there is a supermassive black hole living in the centre of our galaxy. Apparently, supermassive black holes can be found in the centre of most galactic nuclei, and all the stars within the surrounding galactic disk will orbit around it. But how do we know there is a huge black hole in the centre of the Milky Way? What evidence is there? It turns out there is quite a lot, actually.

In a recent review of the subject, the radio emissions observed since the 1950’s are examined. However, probably the most striking piece of evidence is the figure to the left. Of course, we know black holes exert a massive gravitational pull on local space, and by observing the centre of our galaxy, we find there is a huge gravitational influence over a compact cluster of stars, all orbiting a common point, reaching orbital velocities of 5000 km/s…
Continue reading “Meet Sagittarius A*, Our Very Own Supermassive Black Hole”

Hubble Space Telescope observation of Polaris - looking through the Oort Cloud, but not resolving any comets (Hubble) — Hubble Space Telescope observation of Polaris – looking through the Oort Cloud, but not resolving any comets (Hubble)

The Oort Cloud is a mysterious entity. Located on the outskirts of the Solar System, this hypothetical region is probably the source of the long-period comets that occasionally pass through the inner planets’ orbits. The strange thing about these comets is that they have orbits inclined at pretty much any angle from the ecliptic which suggests their source isn’t a belt confined to the ecliptic plane (like the asteroid belt or Kuiper belt). Therefore, their proposed source is a cloud, acting like a shell, surrounding the Solar System.

OK, so we think the Oort Cloud is out there, and there is a lot of evidence supporting this, but why can’t we see the Oort Cloud objects? After all, the Hubble Space Telescope routinely images deep space objects like stars, galaxies and clusters, why can’t we use it to see embryonic comets within our own stellar neighbourhood?
Continue reading “Why Can’t we see the Oort Cloud?”