Base Styles/Icons/Some/Linkedin/Default Created with Sketch. Base Styles/Icons/lock/open Created with Sketch.

Dim light from far-away galaxies deserves a second look

Radio waves are being picked up from galaxies long considered to be silent. What’s up?
Way Out There - Metsähovi Radio Observatory

Most people have just ignored them—the galaxies so quiet or faint that they were deemed silent some two decades ago. It seems that a closer look is worth the trouble, though: some of these same galaxies are surprising researchers by giving off clear and measurable radiation.  

It’s a big, big world 

From our perspective on Earth, our galaxy the Milky Way is huge, with somewhere in the range of 100-400 billion stars. In the grand scheme of things, this massive group is just one drop in a much, much larger sea. Current estimates place the number of galaxies in the observable universe—so the part that we can currently see—at up to 2 trillion.  

Some galaxies, like ours, are pretty normal; the energy they put out can be explained by the stars within their confines. Others are a little more complicated. 

Galaxies can emit various kinds of electromagnetic radiation, including radio, x-rays, ultraviolet light, and microwaves. Since these all occur at different frequencies, tuning into the right wavelength can fill in details of what’s actually happening. That means that if we aren’t watching the right channel, we aren’t seeing the whole picture. 

Radio galaxies emit most of their energy in radio waves—not from stars, like in the Milky Way—so we need to use radio telescopes to see them. The evidence gained so far suggests that radio emissions are coming from plasma jets near the core of each galaxy’s supermassive black hole. From their central spot in the neighbourhood, these jets shoot plasma far and wide, even beyond the boundaries of the galaxy, at nearly the speed of light. 

These systems can actually tell us a lot about galaxies. But because they are so very far away, research has focused on the loudest ones, the galaxies that give off the strongest radio waves, even though these make up only about ten percent of the thousands known.   

 ‘It was a big surprise to detect radio emissions from galaxies that have been labelled radio silent,’ says Anne Lähteenmäki, Professor at Aalto University, who started studying these distant galaxies in 2012. ‘Most studies have concentrated on the bright galaxies instead.’ 

Way Out There - Dim light deserves a second look
Animation: Lukasz Geratowski/Aalto University

Quiet yet powerful 

Anne got curious about fainter signals in her work at Finland’s Metsähovi Radio Observatory. She wanted to take a closer look at the quieter galaxies, the less obvious choices, as a way to study how these gravitationally bound systems evolve. It turns out that young, radio-quiet galaxies provide the perfect context, because they just haven’t had the chance to grow up.  

‘I got interested in their evolution and the various evolutionary lines galaxies could take,’ says Anne. ‘Researchers have always assumed that these galaxies, which are very young, cannot launch plasma jets.’  

Yet all of sudden, evidence showed that they can. It also showed that the masses of central black holes of young galaxies are lower than in brighter sources—roughly a difference of a million of our suns compared to a billion. 

It was a big surprise to detect radio emissions from galaxies that have been labelled radio silent.

Anne Lähteenmäki

So the question is, how do young sources become the really bright, powerful ones?  

Anne’s research has delivered another surprise in the quest for an answer. Not only can so-called radio-silent galaxies produce active jets, they’re spitting out an unexpected kind of energy, gamma rays, typically seen in more mature versions.  

‘You need a lot of energy to create gamma rays. Normally we only see them from elliptical galaxies, which are more evolved, which means these young spiral galaxies are actually really powerful, as well,’ Anne says.  

If Anne’s work highlights one thing, it’s that dedicated eyes and ears, and perhaps a curious mind, will help us understand the universe just a little bit more. The galaxies classified as radio-silent got their labels in one limited all-sky study; her research has shown us why even the quiet ones need attention. After all, with new technologies and the universe as a playground, there are bound to be further developments—and more surprises.  

More from our Way Out There series

Way Out There - Black holes might be nicer than we think
Research & Art Published:

Black holes might be nicer than we think

They’re giant, destructive vacuums with the power to rip stars apart, yet evidence points to the helpful role black holes also play as galaxies form.
Way Out There - space junk
Research & Art Published:

Send it up, up and away? Maybe not, space junk is a problem!

Clearing up the world’s space junk can pave the way for better mobile infrastructure and other ways to move into space
Way Out There - Big blue cylinder
Research & Art Published:

Secrets of our universe live in a big blue cylinder

There isn’t much on Earth but you can find it just about everywhere else — how a type of helium might tell us how everything we know got its start.
Way Out There - Metsähovi Radio Observatory
Research & Art Published:

Dim light from far-away galaxies deserves a second look

Radio waves are being picked up from galaxies long considered to be silent. What’s up?

Related news

Käsi näyttämässä jotain tietokoneen näytöltä
Press releases, Research & Art Published:

Dissertation: Pursuing returns or supporting a cause? Investors are choosing equity crowdfunding for various reasons

The success of equity crowdfunding campaigns depends on many factors, such as campaign characteristics, the company's ability to leverage its networks and how easily understandable the products are, demonstrates a recent doctoral dissertation.
Michael Lettenmeier/photo: Sanna Lehto
Research & Art Published:

Cold choices for a warming planet

A new study from Finland and Japan lays out the massive extent to which our lifestyles need to change if we are to slow down global warming.
Bales of paper and cardboard waste
Research & Art Published:

How to Accelerate the Circular Economy

It sounds simple — one business’s waste becomes another’s input. But the reality is challenging. Three case studies provide best practices.
Aalto University / Aalto satellites family / photo: Linda Koskinen
Cooperation, Research & Art Published:

Virtual world took people to space

The School of Electrical Engineering organised its traditional Research Winter Day on 13 March. This time, research was presented through demos.