Spirals in the Sky

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In my light-flooded city, I see six to seven stars in the night sky. Often, when one refrains from twinkling, I know that it’s a planet – probably either Venus or Mars. These bright stars that I see are probably the ones closer to Earth, but what I look at is the cosmic past. The nearest star system Alpha Centauri is about 4.3 light-years away from Earth and to understand how far that is – it’s 40,208,000,000,000 km away, or roughly 268,770 AU.

Our nearest star system which has 3 stars – Alpha Cen A and B and the third, Alpha Cen C/Proxima orbits the other two. Proxima is the closest star while A & B come second.
Picture Credit – Optical: Zdenek Bardon; X-ray: NASA/CXC/Univ. of Colorado/T. Ayres et al.

Now if the closest star system itself is that far away, think about the closest galaxy.

Our closest major galactic neighbour Messier 31 (also known as Andromeda or NGC 224) roughly 2.5 million light years away from Earth. An estimated 1 trillion stars are there, which is about twice the number we think the Milky Way contains.
Attribution – David (Deddy) Dayag, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0, via Wikimedia Commons

Many galaxies are spiral shaped like our own Milky Way. Some are rugged and irregular – not very captivating to look at, while some others are lenticular galaxies which have very little star formation going on and few others are elliptical galaxies, which are formed when two galaxies collide.

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  NGC 1316 – formed by the merging of two galaxies that contained lots of gases a few billion years ago.

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  NGC 4680 and 2 other galaxies can be seen on the right and bottom of the image. It is classified as either a lenticular or a spiral galaxy.

Picture Credits – Credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA) & ESA/Hubble & NASA, A. Riess et al respectively.

[NGC – New General Catalogue]

Two spiral galaxies NGC 3314a and 3314b. Both are in the same galaxy cluster and when discovered, astronomers thought they were interacting/colliding. But astronomer Bill Keel realized that they were too far away to be interacting. The spiral NGC 3314a is 115 million light-years away and it’s companion NGC 3314b is 140 million light years away.
Picture Credit: NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and W. Keel (University of Alabama)

If those are not colliding galaxies, these are –

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  NGC 4038 & 4039. Their nuclei are just 30,000 light-years apart, 63 million light-years away from us. But this cosmic dance has lead to the formation of more than 1,000 bright star clusters.

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  These two galaxies NGC 2207 & IC 2163 will slowly rip each other apart, which will create several bursts of star formation ending with the smaller galaxy going into the larger.

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  300 million light-years away in the constellation of Coma Berenices, two galaxies are merging. They were once spiral, but will now become one bland elliptical galaxy in a few million years – a blip in cosmic time. They have been nicknamed “The Mice” because of the long tail-like streams of gas and stars emanating from both of them.

Picture Credits – NASA, ESA, and the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration, NASA and The Hubble Heritage Team (STScI), NASA, H. Ford (JHU), G. Illingworth (UCSC/LO), M.Clampin (STScI), G. Hartig (STScI), the ACS Science Team, and ESA (full names have been mentioned at the end); respectively in order- Antennae, NGC 2207 & IC 2163, Mice colliding galaxies.

But these are not colliding-

Picture Credit –  NASA, ESA, S. Beckwith (STScI) and the Hubble Heritage Team (STScI/AURA)

Above is Messier 51, also known as the Whirlpool Galaxy. It’s companion galaxy NGC 5195 had a small graze with M51 70 million years ago. The arms of the Whirlpool give birth to new star clusters. The gravity between the two galaxies created the splendid arms of M51 that we see here. However, these galaxies are no longer connected to each other. They both are just in the same line of sight.

Gravitational forces between two galaxies cause them to collide. The same fate as some of the examples above is predicted to happen to the Milky Way and Andromeda Galaxies roughly four billion years from now. The new galaxy has already been named ‘Milkdromeda’.

Aside from galactic collisions, let us look at a few more stunning galaxies.

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Picture Credit:  Subaru Telescope (NAOJ), Hubble Space Telescope,
European Southern Observatory – Processing & Copyright: Robert Gendler

Meet M83, 40,000 light-years across and one of the closest galaxies, lying about 15 million light years away. It is a ‘barred spiral’ like our own Milky Way and is rich in gas, vigorously using it in star formation. But many of the enormous stars die young. The core of the galaxy shows bright x-ray energies, revealing a large concentration of neutron stars and black holes left from vigorous star formation.

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  This is NGC 7331 – part of a few elite galaxies which help in the measurements of precise distances in the universe. The bright yellow part in the center harbours older, cooler stars. Just like our own galaxy, NGC 7331 hosts a supermassive black hole at its core.

Picture Credit – ESA/Hubble & NASA/D. Milisavljevic (Purdue University)

Finally, I will be ending this post with the spiral NGC 2997. It is home to several millions of elderly stars that are red and yellow, nevertheless the dust lanes near the nucleus signify that the arrival of new stars will still take place. The galaxy lies about 55 million-light years away in the constellation Antlia. It is moving away from us at a rate of 1100 kilometres/second, and with the current estimate for the rate of expansion of the universe, astronomers were able to measure how far away it is.

Picture Credit – FORS Team, 8.2-meter VLT, ESO

So that finishes our post today and I hope you enjoyed looking at some of the spirals that we’ve discovered in the night sky. There are several billion more, but I cannot show all of them to you right away, so I’ve planned to introduce them in future space posts. Anyway, I’ve included some interesting links from which I got some of the information about these galaxies, so you can read those too if you’re interested. (Below the vote buttons)

Also, I’ve added a new page – Random Post Generator , for which I thank Bluefish89 for making the Generator.

Thank you so much for reading!!

Links & Credits –

https://docs.google.com/document/d/1jDaSx8N0ZaG4sJHeZbnZUDzFuS_zq8l5JY6wvZV0uqM/edit?usp=sharing