A guide to the night sky in the coming months part 2 - Globular Clusters

This is positioned in the far south of the sky near the Small Magellanic Cloud (SMC) although not located in that nearby galaxy. It's very much a Milky Way local.

This is a stunning astro object to view in telescopes of all sizes.

It will show as a ball of tightly packed stars in a smaller telescope like the Celestron StarSense Explore LT70 AZ. As the telescope size and power increases in telescopes such as a saxon Dobsonian, more and more stars can be made out.  47 Tuc is home to millions stars and is about 120 light years across. It's over 13 billion years old, which is almost as old as the Milky Way itself.

Under a dark sky, it appears as almost the same diameter as the Full Moon.  47 Tuc is takes up much more any telescope's field of view than even the largest planet, Jupiter. 

Carlos Taylor posted his image of the bright globular cluster 47 Tucanae to the BINTEL Society Facebook Group. He used a 10" Sky-Watcher Quattro Newtonian reflector.

It looks pretty crowded in there. How tightly packed are globular clusters? Do stars ever collide?

Through a telescope globular clusters look dense on their outskirts and seem to be a tightly packed core towards their centres. The stars almost seem to be touching!

However, there's still a huge distance between each star, with around a light year on average and maybe about a third of a light year in the core. This is still vast in human terms. Both of NASA's Voyager spacecraft have been travelling for 40 years but would take them a further 6,300 years to reach the nearest star if it were travelling between stars in the core of a globular cluster. Even with these distances, collisions between stars at the centre of globular clusters are possible. Whether collisions or mergers results in "core collapse" or black holes is still a topic for research. The HST (Hubble Space Telescope) helped us understand how their stars can pull matter from others, effectively winding back their stellar clocks to and forming a brighter star called a "Blue Straggler".

Could life emerge in globular clusters?

Most astrobiologists regard planets as essential for life as we know it to exist and globular clusters are probably not likely places for planets to form. The lack of elements much heavier than hydrogen and helium around their older stars means the materials needed for planets, especially rocky ones like the Earth, simply aren't there*. If planets were to form, they'd probably be yeeted from the globular cluster by gravitational interactions between the stars.

Where did globular clusters come from? 

While our understanding of star formation in a galaxy is generally agreed on, how ancient globular clusters emerge is still not fully clear. A distinguishing feature is that they tend not to have a central black hole - although astronomers have found candidates in some  - nor do they have a halo of dark matter.  Young star clusters in nearby galaxies also don't have these features.

There's no gas and dust in a globular cluster and this means no new stars are now being formed, although some show different populations of stars. What you're viewing is light only from the stars themselves and not from illuminated gas clouds, unlike the emission nebulae we discussed last week.

How can a globular cluster be older than the host galaxy?

Globular clusters are hardy critters. As they're compact (in space terms at least) and so tightly bound together by gravity, as galaxies merge and collide, they're likely to maintain their original form and not be torn apart by the gravitational effects of the encounter. 

Studies by the Gaia mission and other studies have help unravel how the Milky Way was assembled and have discovered more than half of its globular clusters were formed in other galaxies and ended up within it because of mergers.

The Milky Way is the result of multiple mergers with other smaller galaxies. This is quite common for galaxies. While a "galactic merger" sounds like a pretty violent event, they happen over enormous time frames. The stars in galaxies have large distances between each other even in galactic cores so collisions between them would be extremely rare. Think of these events as being more like thin clouds of smoke sliding into each other. The Milky Way and The Andromeda Galaxy will merge in the next few billion years and the globular clusters from the two galaxies will likely settle into the "new" combined entity just fine.

What are some other globular clusters worth exploring?

Here's some of our favourites out of the many that can be seen with even a small telescope. Comment or message me with others you think are worth observing

• M 22 
• 47 Tucanae
• NGC 6752 
• Omega Centauri
• M 62

(You might need to wait for some of these to be visible from your location)

Make sure you point your telescope at a globular cluster in the coming months. They're an amazing sight, with each one being a little bit different. There's nothing like staring at one of these sparkling balls on the edge of our galaxy and realising you're looking at thousands, if not millions of ancient stars from the early days of the Universe.