The blackness, the darkness forever

In many ways, we’re quite lucky to be where we are. Our lovely little blue planet circles a nice calm yellow dwarf star, in a suburban spiral arm, in the midst of the disk of a nice massive spiral galaxy. Things for the Sun are rather pleasant as the Universe goes. We’re not being irradiated by an active galactic nucleus, being threatened by any imminent gamma ray bursts, or in danger of being ejected from the galaxy by any errant black holes or tidal forces from other nearby galaxies. Not all stars are quite so lucky…

We’ve seen stars which are in the process of being flung out of our galaxy. Indeed, thousands of stars are likely being ejected from the galaxy even as we speak. And we live in a rather quiet and peaceful galactic neighbourhood. Galaxies in denser clusters constantly rip at each other gravitationally, casting stars all asunder as they do so.

There are a few different paths that stars can take on their perambulations from their galactic home. Some are merely wanderers. They stay loosely bound by the galaxy’s gravitational pull, they may wander deep into intergalactic space (probably enjoying a wonderful view of the galaxy from out there), before eventually falling back into the midst of its brethren stars. Some remain loosely gravitationally tied to the galaxy, but never return home. Some are simply ejected to roam aimlessly through the dark. The night time skies on any planets orbiting these worlds would be dark indeed. There would be not a single star in the sky. If Earth was in such a situation, then other than the moon, we’d see only the other planets, and the vague fuzzy shapes of galaxies in the distance. The night sky would be nearly pitch black. Just imagine a sky without stars…

It’s conservatively estimated that 0.05% of all stars may be just such intergalactic stars (sometimes referred to as “tramp stars”). Seemingly a small percentage, but 0.05% of billions is still huge number. In fact, in the Virgo cluster where intergalactic stars* were first discovered, up to one trillion such stars are expected to exist. In other words, there are more stars between the galaxies in the Virgo cluster than there are in any single one of the 2500 galaxies in the cluster, accounting for around 10% of the cluster’s total mass. And the Virgo cluster isn’t unique. A similar intergalactic population of stars has also been found in the Fornax cluster. They probably exist in other clusters too. This population of lonely stars even results in intergalactic planetary nebulae, and intergalactic classical novae. I sometimes wonder what secrets lie waiting out in the darkness, for us to discover…

*I’m sure any of my galaxy-loving friends would tell me that these should technically be referred to as intra-cluster stars.

About Invader Xan

Molecular astrophysicist, usually found writing frenziedly, staring at the sky, or drinking mojitos.
This entry was posted in Imported from Livejournal and tagged , . Bookmark the permalink.

3 Responses to The blackness, the darkness forever

  1. I wonder how astronomy would develop on a planet orbiting an intergalactic star?

  2. pax_athena says:

    Aye, those are really fascinating. And all the fancy stuff one can study with them – e.g. the dark matter distribution *_* (Well, I mainly know because one of the guys here is working on hypervelocity stars in our own Milky Way).

  3. Anonymous says:

    I smelled like an old person. :|

Comments are closed.