Small but Mighty

In January, whilst on my morning walk to the train station, I spotted two bright spots in the sky near the moon. After a week of these sightings, it turns out they were Jupiter and Venus taking centre stage at 7am on those dark winter mornings. On a planet home to 7.7 billion people going about their daily lives, I was seeing Jupiter and Venus on my way to work. We are only in this universe for a relatively tiny amount of time and yet so lucky to live amongst it all with knowledge at our fingertips. It got me thinking, what are the coolest things known about our home galaxy, the Milky Way?

What is the shape of the Milky Way? Contrary to popular belief (and much documented science fiction) a report last month (Feb’19) ruled that the Milky Way is in fact not flat but warped and twisted [1]. The researchers used 1,339 Cepheid stars (i.e. stars which brighten and dim according to the energy they are emitting) to calculate their distances from Earth and thus, create a true map of the galaxy. Findings showed the further the stars were from the centre of the spiral galaxy, the more warped the structure becomes. It was a difficult task, researchers compared it to “standing in your garden in Syndey and trying to map Australia” [2].

The Milky Way is a spiral and has various arms; our solar system sits in a smaller spur called the Orion Arm, located between larger arms, Perseus and Sagittarius. Much like the Earth moves around the Sun, the Milky Way is not a stationary thing either, it is constantly rotating. As such, our solar system is moving with the galaxy at an average speed of 515,000 mph [3], but would it would take us 230 million years to travel the entire way around. The Milky Way is 100,000 light years in diameter; it’s pretty big. As the spiral arms move, gas and stars crowd together backing up like cars in a traffic jam, and as more material passes through the arms it all becomes condensed and eventually leads to new star formation [3].

Most fascinating of all is the gigantic black hole at the centre of the Milky Way [4]. Much like the Muse song, it is a Supermassive black hole, billions of times as massive as our sun but with a similar radius. Gas and dust which surrounds this area of the galaxy forms a buffet for the black hole to feast on, enabling it to grow to today’s extraordinary mass. We cannot directly observe black holes, but their gravitational effects can be detected, and it is thought that most galaxies have one at their centre. It is still not known for certain how Supermassive black holes form: it could be the accumulation of many smaller black holes, the collapse of huge gas clouds gathering mass, or the fall of a cluster of stars all at once.

There are an estimated 100 billion galaxies in the Universe that Hubble has revealed, although this is likely to increase to 200 billion as technology improves. I think it’s incredible that we live on one perfect planet to sustain our lives, in one galaxy amongst possibly 200 billion others. We are small but mighty.

This was an article originally written in March 2019 for the Science Geekette blog run by Hollie Wright who you can find here: https://instagram.com/hollieforscale

References:
[1] X. Chen, S. Wang, L. Deng et. al. An intuitive 3D map of the Galactic warp’s precession traced by classical Cepheids. Nat. Astro. (2019).
[2] D. Byrd https://earthsky.org/space/milky-way-warped-twisted-study-cepheids (2019)
[3] N. Redd https://www.space.com/19915-milky-way-galaxy.html (2017)
[4] R. Genzel https://www.eso.org/public/news/eso1835/?lang (2018)

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