Galaxy count has just spiked | Science News for Students

Galaxy count has just spiked

New census suggests the universe may have 10 times as many galaxies as astronomers had estimated
Oct 31, 2016 — 7:00 am EST
distant galaxies

This image shows very distant galaxies. Using such images, astronomers came up with a new tally of how many galaxies have ever existed: 2 trillion.


There may be a whole lot more massive communities of stars out there for future telescopes to explore. That’s the conclusion of a new survey of the universe. It estimates there may have been as many as two trillion galaxies. This new count is roughly 10 times the earlier estimate.

Christopher Conselice and his team posted their new estimate online October 10 at

Conselice works at the University of Nottingham in England. As an astrophysicist, he studies the physical nature of stars and other objects in space. Galaxies are enormous collections of stars, each potentially containing trillions of stars and more. To perform its new galaxy count, Conselice’s group worked with images from a series of telescopes. These included the Hubble Space Telescope.

The team used a computer to turn the images into three-dimensional models of the universe. Each would model a different time in the history of the cosmos. The goal was to tally the likely number of galaxies at those different points in time to calculate how the galaxy count might had changed.

The team also did mathematical work. That allowed them to account for extremely faint galaxies — ones too faint for any existing telescope to pick up.

The final count proved far higher than the earlier estimate of some 200 billion galaxies. Many tiny galaxies appear behind the newfound increase. These mini galaxies might weigh as little as 1 million suns. Keep in mind, astronomers have not yet laid eyes on  such runts. They are simply too far away for even the best telescopes to spot.

But one day they might. Light from even the earliest and most distant stars and galaxies continues to zoom around the universe. The runt galaxies in question probably existed in the early universe. Back then, it is likely that there were far more galaxies than exist today. Conselice’s team drew that conclusion from its results.

Its analyses suggest that the number of galaxies has fallen with time. Most of the 2 trillion that likely existed at some point collided and merged. The result were gargantuan mega-galaxies. Such biggies include the Milky Way. Galactic mergers are, in fact, in line with prevailing ideas about how massive galaxies come to be.

To confirm the new count, astronomers will need more powerful eyes to scan the skies. If those telescopes are sensitive enough, they might one day pick up light from the distant, early universe. Their powerful optics might confirm the existence of numerous early, runt galaxies. But that will take some time, the researchers point out: “We will have to wait at least several decades before even the majority of galaxies [show up].”


Power Words

(for more about Power Words, click here)

arXiv     A website that posts research papers — often before they are formally published — in the fields of physics, mathematics, computer science, quantitative biology, quantitative finance and statistics. Anyone can read a posted paper at no charge.

computer model     A program that runs on a computer that creates a model, or simulation, of a real-world feature, phenomenon or event.

galaxy     A massive group of stars bound together by gravity. Galaxies, which each typically include between 10 million and 100 trillion stars, also include clouds of gas, dust and the remnants of exploded stars.

mega     A prefix for units of measurement meaning million in the international metric system. Also colloquially used as an adjective to mean some really large, imprecise number.

Milky Way     The galaxy in which Earth’s solar system resides.

optics     Having to do with vision or what can be seen.

physical     (adj.) A term for things that exist in the real world, as opposed to in memories or the imagination. It can also refer to properties of materials that are due to their size and non-chemical interactions (such as when one block slams with force into another).

runt     An organism that starts its life much smaller than usual, and may stay smaller than normal into adulthood. 

star     The basic building block from which galaxies are made. Stars develop when gravity compacts clouds of gas. When they become dense enough to sustain nuclear-fusion reactions, stars will emit light and sometimes other forms of electromagnetic radiation. The sun is our closest star.

sun     The star at the center of Earth’s solar system. It’s an average size star about 26,000 light-years from the center of the Milky Way galaxy. Or a sunlike star.

telescope     Usually a light-collecting instrument that makes distant objects appear nearer through the use of lenses or a combination of curved mirrors and lenses. Some, however, collect radio emissions (energy from a different portion of the electromagnetic spectrum) through a network of antennas.

trillion     A number representing a million million — or 1,000,000,000,000 — of something.

universe     The entire cosmos: All things that exist throughout space and time. It has been expanding since its formation during an event known as the Big Bang, some 13.8 billion years ago (give or take a few hundred million years).

Read another version of this article at Science News


Journal:​ C.J. Conselice et alThe evolution of galaxy number density at z < 8 and its implications. arXiv: 1607.03909. Published online October 10, 2016.