Astronomers discover vast ancient galaxies, which could shed light on dark matter

A long time ago, galaxies far, far away
Ancient galaxies from the study are visible to ALMA (right) but not to Hubble (left). Credit: (c) 2019 Wang et al.

Astronomers have used the combined power of multiple astronomical observatories around the world and in space to discover a treasure trove of previously unknown ancient massive galaxies. This is the first multiple discovery of its kind, and such an abundance of this type of galaxy defies current models of the universe. These galaxies are also intimately connected with supermassive black holes and the distribution of dark matter.

The Hubble Space Telescope offered unprecedented access to the previously unseen universe, but even it is blind to some of the most fundamental pieces of the cosmic puzzle. Astronomers from the Institute of Astronomy at the University of Tokyo wanted to observe objects they long suspected were out there, but which Hubble could not reveal. Newer generations of astronomical observatories have finally revealed what they sought.

"This is the first time that such a large population of massive was confirmed during the first 2 billion years of the 13.7-billion-year life of the universe. These were previously invisible to us," said researcher Tao Wang. "This finding contravenes current models for that period of cosmic evolution, and will help to add some details, which have been missing until now."

But how can something as big as a galaxy be invisible to begin with?

"The light from these galaxies is very faint, with long wavelengths invisible to our eyes and undetectable by Hubble," explained Professor Kotaro Kohno. "So we turned to the Atacama Large Millimeter/submillimeter Array (ALMA), which is ideal for viewing these kinds of things. I have a long history with that facility, and so knew it would deliver good results."

A long time ago, galaxies far, far away
A few of the 66 radio telescope antennas that make up ALMA. Credit: (c) 2019 Kohno et al.

Even though these galaxies were the largest of their time, their light is not only weak, but also stretched due to their immense distance. As the universe expands, light passing through becomes stretched, so becomes longer, eventually becoming infrared. The amount of stretching allows astronomers to calculate how far away something is, which also reveals how long ago the light was emitted from the object.

"It was tough to convince our peers that these galaxies were as old as we suspected them to be. Our initial suspicions about their existence came from the Spitzer Space Telescope's infrared data," said Wang. "But ALMA has sharp eyes, and reveals details at submillimeter wavelengths, the best wavelengths to peer through dust present in the early universe. Even so, it took further data from the imaginatively named Very Large Telescope in Chile to really prove we were seeing ancient massive galaxies where none had been seen before."

Another reason these galaxies appear so weak is because larger galaxies, even in the present day, tend to be shrouded in dust, which obscures them more than their smaller galactic siblings.

And what does the discovery of these massive galaxies imply?

"The more massive a galaxy, the more massive the supermassive black hole at its heart. So the study of these galaxies and their evolution will tell us more about the evolution of supermassive black holes, too," said Kohno. "Massive galaxies are also intimately connected with the distribution of invisible dark matter. This plays a role in shaping the structure and distribution of galaxies. Theoretical researchers will need to update their theories now."

A long time ago, galaxies far, far away
Professor Kotaro Kohno. Credit: (c) 2019 Rohan Mehra - Division of Strategic Public Relations

Astronomers are also interested in how these 39 galaxies differ from our own. If our were inside one of them and you were to look up at the sky on a clear night, you would see something quite different to the familiar pattern of the Milky Way.

"For one thing, the night sky would appear far more majestic. The greater density of stars means there would be many more stars close by appearing larger and brighter," explained Wang. "But conversely, the large amount of dust means distant stars would be far less visible, so the background to these bright close stars might be a vast dark void."

As this is the first time such a population of galaxies has been discovered, the implications of their study are only now being realized. There may be many surprises yet to come.

"These gargantuan galaxies are invisible in optical wavelengths so it's extremely hard to do spectroscopy, a way to investigate stellar populations and chemical composition of galaxies. ALMA is not good at this, and we need something more," concluded Wang. "I'm eager for upcoming observatories like the space-based James Webb Space Telescope to show us what these primordial beasts are really made of."

Explore further

Hubble observes tiny galaxy with big heart

More information: T. Wang, C. Schreiber, D. Elbaz, Y. Yoshimura, K. Kohno, X. Shu, Y. Yamaguchi, M. Pannella, M. Franco, J. Huang, C.F. Lim & W.H. Wang. A dominant population of optically invisible massive galaxies in the early Universe. Nature. DOI: 10.1038/s41586-019-1452-4 ,
Journal information: Nature

Citation: Astronomers discover vast ancient galaxies, which could shed light on dark matter (2019, August 7) retrieved 18 August 2019 from
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.

Feedback to editors

User comments

Aug 07, 2019
This comment has been removed by a moderator.

Aug 07, 2019
But the "bow waves" are the visible matter, not the dark matter. That doesn't make any sense.

Aug 07, 2019
What's with the "let's trash Hubble" aspect of this article? It wasn't even necessary to mention it to discuss this data. Yet, whoever authored this piece felt the need to denigrate its capabilities.

What was the purpose?

Aug 07, 2019
Well, speaking only for what's being said around Hawai'i -- it's very common for ignorant people to say things like "why build another ground-based telescope when we have Hubble and James Webb?" and "the space telescopes tell us everything we need to know."

These statements get trotted out here in discussions of the Thirty Meter Telescope. People who don't know know any better say, "Yeah!"

So although I can't know the author's intent, I do suspect it's to lay down statements against the myth that space telescopes can do everything.

Aug 07, 2019
i dunno Ophelia,
my impression of the comments about the Hubble telescope seemed factual & not exaggerated

they even admitted that the present day machinery would soon be obsolete compared to the Webb & other hoped for improvements in astronomical technology, yet to come.

but we don't give up backyard telescopes or binoculars just because these are hopeless;y outclassed by standards if advancing sciences

knock on vinyl... the Hubble will still be producing productive photographs as long as anyone is sentimental enough to keep it running

"time & tide await no man
or even a feisty little robot"

sooner or later, for all of us
our batteries will run down
& the command line will go unresponsive

Aug 07, 2019
There are some very complicated issues of galaxy formation. Unfortunately, here is the same problem as with the stars. The origin of galaxies remains unclear, in spite of huge activity in the field. What the "formation" means? It means that we have the material that is assembling into galaxies.

Aug 07, 2019
This article is oddly written. It is akin to an article talking about laser fusion being attempted at one DOE lab and pointing out that the US Department of Agriculture can't do the same. What would be the point? Except to jab the USDA for some reason, even if what was being said was accurate.

I'm certainly not a conspiracy nut, but the entirety of the Hubble discussion was extraneous to the core of the article, so what was the reason to include what basically amounted to jabbing Hubble in its metaphorical ribs?

Just seems to me that someone has a grudge - or doesn't know how to write a science article.

Aug 08, 2019
Dark matter

Aug 08, 2019
well. i can't imagine anyone having a grudge against a space telescope?
maybe a religious believer, begrudging their tax money being spent on the devilish machine?
& they didn't even get any photo's back of the Heavenly Host waving at them?

many of us have complained of the mediocre writing & editing but that is the price of free articles available online from a multitude of sources...
click the ads, they pay the bills

you've heard the joke
"what do you call the lowest ranking student, hindmost in line at a medical school graduation ceremony?"
"why, you call him Doctor!"

& if there was any intent meant to mentioning the Hubble?
it sounded to me like a plea to continue or perhaps, renew funding for their research program?

big research takes big budget
with all the other projects out there clamoring for funding?
this ain't no time to be shy & retiring about your team's needs!

the business of academics is too earn a living
preferably getting paid to do interesting work

Aug 08, 2019
Another dark matter fail. Zero wins, all loses but the acolytes still cheer it on. LOL!

Aug 08, 2019
Another dark matter fail. Zero wins, all loses but the acolytes still cheer it on. LOL!

As opposed to the Velikovsky acolytes who cheer on claims of Venus hurtling around the solar system after being ejected by Jupiter! Or Earth formerly orbiting Saturn! Among other scientifically impossible woo. No lessons to be learned from clowns like that.

Aug 08, 2019
A fantastic find, if it can be confirmed! Earlier observation found a scarcity of galaxies, and it is my understanding [ see this review: https://www.scien...s-cosmic ] that star and galaxy formation that is the large uncertainty of cosmological modeling. It seems it is here that modelers have used most semi-analytic models while at the same time modified them most to fit what astronomers see.

To wit, from the paper: "The early formation of such a large number of massive, dusty galaxies is unexpected with current semi-analytical models, which underestimate their density by one to two orders of magnitude (Fig. 3)."

- tbctd -

Aug 08, 2019
- ctd -

While from the review: ""Perhaps the simulations' single biggest lesson so far is not that scientists need to revise their overarching theory of cosmology, but rather that problems lurk in their understanding of astrophysics at smaller scales. In particular, their theory of star formation comes up wanting, Springel says. To produce realistic galaxies, modelers must drastically reduce the rate at which clouds of gas form stars from what astrophysicists expect, he says. "Basically, the molecular clouds form stars 100 times slower than you'd think," he says.""

Possibly then the modelers adjusted star formation rates down 2 orders of magnitude to fit the earlier observed galaxy density in the early universe. But the new observation may give a rationale to increase that rate with a corresponding factor.

Aug 08, 2019
thanks torbjorn for clarifying those issues

i could not understand what seemed to me (vaguely)
to be either a contradiction
or an inconsistency

won't claim total grasp of the subject but your help chivvied my mind a little further on!

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more