Scientists aren’t exactly sure if galaxy creation has come to an end in our universe.
It’s an active area of research, so active that the James Webb Space Telescope, launched only months ago as this article is published, is involved in answering questions about galaxy mergers and formation
We know that new stars are still being created within galaxies in prodigious quantities. What we’re not certain of is whether new galaxies are being created today and, if they are, whether they are being created at the same rate as in the far distant past?
In this article, we’re going to look at what today’s best evidence tells us about galactic formation today.
Is There Enough Material to Create New Galaxies?
We begin with considering whether there is enough material left in the universe to create new galaxies because we know that they are staggeringly huge and there is a mind-blowing number of galaxies out there.
Have they taken up all the matter that exists in the Universe, leaving none behind for new galaxy formation?
The short answer is no!
Astrophysicists believe that less than 10% of all ordinary (baryonic) matter is in stars in galaxies. Some more may be within the sphere of influence of a galaxy, which can extend to millions of light-years.
Yet 40-50% of matter is thought to be very thinly spread throughout the space between the galaxies. This matter is known as the warm-hot intergalactic medium (WHIM) and is much more sparse than galaxies, which themselves are mostly empty space.
While the WHIM is thought to be too sparsely spread to ‘clump’ together to form new solar systems and galaxies, there is more than enough of it, in theory at least, enough material to form new galaxies.
We know, then, that the material exists to create new galaxies. Let’s consider next how they are formed.
How Massive Galaxies are Created
We believe that the largest galaxies were formed from the merger of smaller galaxies, which in turn formed from protogalaxies. Protogalaxies were born from the first massive stars created 100-200 million years after the Big bang.
This is known as the bottom-up theory of galaxy formation.
Using clever gravitational lensing techniques, astronomers have found evidence that the very early universe was full of small galaxies, giving weight to this theory.
Merging Galaxies
There is a huge volume of evidence that supports the theory that smaller galaxies merge – or larger galaxies ‘eat’ smaller ones – to form yet larger galaxies.
When you consider the numbers, galactic collisions are likely to occur frequently, on a galactic timescale, at least.
The universe is crowded at the galactic scale. Andromeda and the Milky Way, for example, are only 25 times further apart than the size of the galaxies, and they are travelling through space, which is why collisions are not uncommon, as photographic evidence demonstrates.
Andromeda Galaxy and the Milky Way are orbiting a common barycenter and will collide in four and a half billion years and merge over another 6 billion years or so to form a new mega-galaxy at the cost of two existing large ones.
And this won’t be the Milky Way’s first brush with another galaxy or even its next!
The Milky Way has gobbled up a dozen galaxies before and is in the process of merging with three others right now, including the Large and Small Magellanic clouds.
If your definition of a new galaxy is one born from the merger of two others, then we can say with certainty that galaxy formation is still very active today.
Check out the images of the Whirlpool Galaxy (above) and the Butterfly Galaxies, below, for a small sample of the galaxy merger process in action. You can observe these for yourself using a telescope for looking at galaxies (opens a new tab).
However, if the question is more rigorous, i.e. are brand new galaxies still being created, then the answer is more nuanced.
Are Brand New Galaxies Still Forming Today?
There is no evidence for modern protogalaxy formation. However, baby galaxies as young as 100 million years old were seen by NASA’s Galaxy Evolution Explorer satellite. The closest is 2 billion light-years away, suggesting new large galaxies are still being created today.
The Galaxy Evolution Explorer (Galex) ended its official lifespan in 2013. It was designed to measure the history of star – and hence, galactic – formation in the early universe.
It didn’t spy any protogalaxies, and neither has any other telescope since. Protogalaxies are thought to have formed just a few hundred million years after the Big Bang. These are the huge clouds of gas that are collapsing through vigorous star formation into galaxies.
On its own, that suggests that the process of galaxies popping into existence (over hundreds of millions of years) from gas clouds has probably ended.
However, we do see baby galaxies in large enough numbers to suggest that the story of early galactic formation is still very current.
Not only did Galex find at least 24 baby galaxies, but the Hubble Space Telescope also found one only 45 million light-years away.
Tim Heckman, part of the research team at Astrophysical Sciences at Johns Hopkins University, said of Galex’s discovery “What we’re seeing right now is perhaps the last dregs of galaxy birth, the last few stragglers,” he said. “We don’t yet know really what’s controlling this decline in the formation of galaxies.”
When Was the Last Galaxy Formed?
Scientists have known for a long time that most large galaxies were born 5-10 billion years ago and the rate of their creation has been in decline since.
The most recently formed galaxy is believed to be the one in this report with the catchy name HSC J1631+4426, which is 460 million light-years away and thought to be less than half-a-billion years old, compared to our own galaxy’s 13.6 billion years.
Summary
There is no evidence of protogalaxy formation happening today. Protogalaxies are the precursor of galaxies and not seeing them suggests galaxy formation has come to an end.
Scientists have, however, found tantalizing evidence of ‘baby galaxies’ relatively nearby. This leads astronomers to believe that the maturing of young galaxies has not yet come to an end.
Outside of those scant examples of genuine new galaxies, all we have left is the merger of existing galaxies leading to new star birth from the violent energy that ensues.
What we don’t know yet is what the James Webb telescope will discover about the current state of galaxy creation when it sees further back in time than we’ve ever managed before.
Further Reading
This article from Space Australia (link opens a new tab) gives a fascinating insight into how astronomers look for young, far-distant galaxies.
