Universe contains ten times more galaxies than previously thought

Our universe just became even more crowded. A deep-sky census derived from the images taken by the Hubble Space Telescope found that the observable universe contains at least ten times more galaxies than astronomers previously thought and that it houses no less than 2 trillion galaxies. The surprising finding, based on sophisticated 3D modelling of images collected over 20 years by the Hubble Space Telescope, was published in the Astrophysical Journal.

The universe is mind-bogglingly vast. Therefore, when observing the objects within it, Earth-bound astronomers can see only the part of space from where light given off by distant stars and galaxies has had time to reach our planet. The rest is effectively beyond our reach. And even within this ‘observable universe’, current technology only allows us to glimpse mere 10% of what is out there, according to the new findings.

Sizes of galaxies vary wildly – from dwarf galaxies containing only a few billion stars, such as I Zwicky 18 (pictured on the left) to behemoths like Condor Galaxy (pictured on the right) which could contain upwards of 2 trillion stars.

The in-depth survey, based on the scrutiny of photographs obtained by the Hubble Telescope, shown that we had grossly underestimated the number of galaxies in our universe – in fact by a factor of 10.

Christopher Conselice of the University of Nottingham, United Kingdom, who led the study, said: “It boggles the mind that over 90% of the galaxies in the [observable] universe have yet to be studied.”, before continuing: “Who knows what interesting properties we will find when we observe these galaxies with the next generation of telescopes?” One of these ‘next generation telescopes’ is Hubble Space Telescope’s successor, the James Webb Space Telescope, which, if all goes according to the schedule, should be deployed in October 2018 and will be able to peer much further into the blackness of space than its predecessor, giving astronomers the much sought-after tool to explore more of these remaining 90% galaxies, currently all but beyond their reach.

Astronomers and Astrophysicists have puzzled over how many galaxies our universe harbours since 1924, when US astronomer Edwin Hubble established that the nearest major astronomical object – Andromeda, is in fact not just another star in our own galaxy – Milky Way, but a completely separate grouping of stars. But even in the era of modern astronomy, getting an accurate count of how many galaxies there actually are, has proven very difficult.

Until the recent study, the best estimate of the number of galaxies in the universe has been around 200 billion. This number was based on a 1996’s Hubble Deep Field study, in which astronomers pointed the Hubble Space Telescope at a small, seemingly empty, region of space in the constellation Ursa Major for a total of ten days so that the long exposure would reveal extremely faint objects in the far distance.

The photo revealed more than 3,000 distant objects, most of them galaxies – some among the youngest and most remote ones known to date – up to 12 billion light years away, capturing them as they existed less than two billion years after the Big Bang. Although some galaxies in the photo are only a few pixels across, both irregular and spiral galaxies are clearly visible. Astrophysicists then extrapolated the number of galaxies to the whole sky, under the assumption that their distribution would be similar in all directions, to arrive at the 200 billion figure.

The Hubble Deep Field photograph (taken by Hubble Space Telescope, inset) covered only about one 24-millionth of the whole sky, yet it revealed close to 3,000 youngest and most distant galaxies, thus becoming a landmark picture in the study of the early universe.

However, there clearly weren’t enough galaxies in the Hubble Deep Field image to account for the estimated density of matter distributed throughout the universe. The missing matter had to be in the form of galaxies too faint to see, interstellar gas, dust and the mysterious dark matter. “We always knew there were going to be more galaxies than that.” said Conselice, before adding: “But we didn't know how many existed because we couldn’t image them.”

Our universe just got 10x more crowded – astrophysicists reckon that it contains at least 2 trillion galaxies – that is ten times more than was previously thought.

To correct this apparent discrepancy, Conselice and his team took deep space images from Hubble Telescope and painstakingly converted them into 3D in order to estimate the number of galaxies at different times in the history of the universe. This, more precise analysis, reached back further than 13 billion years – shortly after the time of the Big Bang that is thought to have given birth to the universe.

In the study published in the Astrophysical Journal, Conselice and his team explain how they, using the images from Hubble Telescope as well as other observatories, counted the visible galaxies out to distance of 13 billion light years. This enabled them to plot the number of galaxies of a given mass that corresponded to various distances from Earth. The researchers then extrapolated their estimates to encompass galaxies too small and too faint for telescopes to pick up. Based on this research, they were able to calculate that the whole observable universe should contain at least 2 trillion galaxies – 10 times more than previously thought.

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So, can we now finally say if there really is more stars in universe than grains of sand on all beaches?

At the first glance, it seems nigh on impossible to prove or disprove this age-old adage. However, even a seemingly impossible task becomes solvable if we take a step-by-step approach, and break our ostensibly ‘impossible’ task into a few, still difficult but scientifically solvable, parts.

Because, rather conveniently, the above study presents us with a nice starting point, let’s begin with the number of stars in the universe. We already know that the observable universe contains somewhere in the region of 2 trillion galaxies – but what is the number of stars in an average galaxy? To answer this question, we must first fully understand what galaxies are, and how they are classified by astronomers.

Galaxies – which are enormous, gravitationally bound systems of stars, with planetary systems, such as ours, as well as stellar remnants, interstellar gas and dust within them – range in size from dwarfs composed of ‘measly’ hundreds of million to several billion stars, to giants that contain up to hundred trillion stars. The typical example of a dwarf galaxy is I Zwicky 18 located about 59 million light-years away in the constellation Ursa Major, composed of a ‘mere’ few hundred million stars. Our own galaxy, Milky Way, by all standards an average-sized galaxy housing between 200 and 400 billion stars, lies somewhere in the middle of this scale. On the other side of the range are giant galaxies such as NGC 6872. This super-massive spiral galaxy also known under the name Condor Galaxy, which is located about 212 million light-years from Earth, has been known to astronomers for decades. But it wasn’t until a recent survey of nearby star-forming regions that NASA scientists realised just how big it truly is. New data shows that, from tip-to-tip across its two outsized spiral arms, this enormous galaxy measures a whopping 522,000 light-years across – making it more than five times the size of the Milky Way. NASA now says NGC 6872 is the largest spiral galaxy that has ever been discovered, and, assuming it has a similar star distribution to the Milky Way, it could contain up to 2 trillion stars. But even this galactic behemoth is all but dwarfed by IC 1101 – a super-giant elliptical galaxy at the centre of the Abell 2029 galaxy cluster, approximately 1 billion light-years from Earth, that contains roughly 100 trillion (!!!) stars.

It might be a mind-boggling notion, but now it is a scientific fact: there really is more stars in the universe than grains of sand on all the beaches on our planet.

If we take the number 100-500 billion to represent the median number of stars in an average galaxy and multiply this by the aforementioned 2 trillion galaxies that are thought to be present in the observable universe, we arrive at the astronomical figure (if you pardon my pun) of anything between 200 sextillion (200 followed by 21 zeros) to 1 septillion (1 followed by 24 zeros) stars in our universe.

It boggles the mind that over 90% of the galaxies in the universe have yet to be studied – Christopher Conselice, publisher of the study

It is a tad more complicated with sand, since its grains vary vastly, but let’s assume a typical grain of sand has an average size of about half a millimetre. Therefore, you could lay 20 grains of sand side-by-side to make a centimetre. Simple calculation 20x20x20=8,000 then gives us the number of sand grains in one cubic centimetre. There is 1,000,000 cubic centimetres in a cubic metre (100x100x100) and when we multiply this by our 8,000 grains of sand in a cubic centimetre, we get number of sand grains in a cubic metre – 8,000,000,000, or 8 billion. It has been estimated that the total volume of sand on all the beaches of the planet Earth is about 700 billion m3. Hence, finally, we must multiply 700 billion by 8 billion, giving us 'mere' 5.6 sextillion (5 followed by 21 zeros) grains of sand on all the world’s beaches.

And the conclusion? It is a mind-boggling thought, something our imagination may really struggle to fathom, but there really is more stars in the universe than grains of sand on all the beaches on our planet – in fact, just about 100 times more!