{"id":55170,"date":"2024-02-14T14:06:31","date_gmt":"2024-02-14T14:06:31","guid":{"rendered":"http:\/\/07d66db7-0829-43f0-88d1-ed6e89c99bbb"},"modified":"2024-02-14T14:32:32","modified_gmt":"2024-02-14T14:32:32","slug":"galaxies-are-moving-away-at-an-increasing-rate-carried-by-the-expansion-of-the-universe","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/rss_feed\/galaxies-are-moving-away-at-an-increasing-rate-carried-by-the-expansion-of-the-universe\/","title":{"rendered":"Galaxies are moving away at an increasing rate, carried by the expansion of the Universe"},"content":{"rendered":"

If the Universe is expanding, does that mean all galaxies will be torn apart? <\/p>

By Alastair Gunn\n <\/p>

Published: Wednesday, 14 February 2024 at 14:06 PM<\/p>

\n\n

All galaxies move. The motions of galaxies can be measured using the Doppler Effect<\/a>, which changes the wavelength of light emitted by a galaxy due to its motion relative to us.<\/p>

A galaxy<\/a> moving away from us is \u2018redshifted<\/a>\u2019 while a galaxy moving towards us is \u2018blueshifted\u2019.<\/p>

Since all the light from a moving galaxy is shifted by the same relative amount, astronomers make use of \u2018spectral lines\u2019 in this process.<\/p>

Chemical elements in the galaxy emit or absorb light at certain well-defined wavelengths and effectively act as markers within the galaxy\u2019s light spectrum.<\/p>

The shift in the spectral lines reveals the galaxy\u2019s velocity relative to us.<\/p>

The further away a galaxy is, the more its light is shifted to longer wavelengths \u2013 an effect known as redshift<\/figcaption><\/figure>

Galaxies’ motion and the expansion of the Universe<\/strong><\/h2>

In general, galaxies are moving away from each other at an ever increasing rate, carried along by the expansion of the Universe<\/a>.<\/p>

The further away a galaxy is from us, the faster it is moving away.<\/p>

This relationship between distance and \u2018redshift\u2019 is known as the Hubble-Lema\u00eetre Law.<\/p>

The discovery that the Universe is expanding led to the development of the Big Bang theory of the Universe.<\/p>

\"As
As light travels through expanding space, it is stretched to longer wavelengths. Credit: NASA, ESA, Leah Hustak (STScI)<\/figcaption><\/figure>

Does this mean galaxies will be torn apart?<\/strong><\/h2>

Cosmic expansion is only noticeable over scales comparable to the size of galaxy clusters<\/a>.<\/p>

The gravitational interaction between galaxies on these scales is insufficient to prevent them from moving apart.<\/p>

But on much smaller scales, the gravitational forces between galaxies can be large enough to overcome the cosmic expansion, allowing galaxies to interact, collide and sometimes merge.<\/p>

For example, in our own \u2018Local Group\u2019 of galaxies<\/a>, which also includes the Andromeda Galaxy<\/a> and the Large and Small Magellanic Clouds, some galaxies are moving away from us (redshifted) and some toward us (blueshifted).<\/p>

\"The
The distorted shapes and tails of some of the galaxies in the group known as Stephan’s Quintet are evidence of them having had close interactions with each other. Credit:NASA, ESA and the Hubble SM4 ERO Team<\/figcaption><\/figure>

The Local Group of galaxies is, as a whole, moving through space at about 630 km\/s.<\/p>

Members of the group are also moving towards the Virgo cluster of galaxies at between 100 km\/s and 400 km\/s.<\/p>

But our closest large galactic neighbour, the Andromeda Galaxy, is heading towards the Milky Way at around 120 km\/s.<\/p>

The latest research suggests Andromeda will collide almost head-on with the Milky Way in about 4 billion years! This event is known as the Andromeda-Milky Way collision.<\/p>

The highest blueshift yet recorded is actually from a group of stars called a \u2018globular cluster\u2019 that resides near the galaxy M87; twenty times further away than the Andromeda Galaxy!<\/p>

\"A
A simulation showing Earth\u2019s night sky in 3.75 billion years as Andromeda collides with the Milky Way. Credit: NASA; ESA; Z. Levay and R. van der Marel, STScI; T. Hallas; and A. Mellinger<\/figcaption><\/figure>

Galaxies move…and rotate<\/strong><\/h2>

We’ve seen how astronomers can show that galaxies move, but what about their rotation?<\/p>

To measure a galaxy\u2019s rotation, astronomers look at light from opposing sides of the galaxy.<\/p>

One side is approaching us while the other is receding (once the galaxy\u2019s overall motion is accounted for) and that difference reveals the rotation speed of the galaxy.<\/p>

Typical rotation speeds in the outer regions of galaxies are several hundred km\/s.<\/p>

In the 1970s, astronomers found that galaxies rotate in a way that cannot be driven purely by visible matter.<\/p>

That is, the velocity of stars remains the same throughout a galaxy, rather than dropping off with distance from the centre, as would be expected.<\/p>

This discovery led to the hypothesis that some other type of invisible matter must be acting on distant stars to give them an added push.<\/p>

That invisible matter we now call \u2018dark matter<\/a>\u2019.<\/p> <\/body><\/html>\n

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