Modern Australian
Men's Weekly

.

Some black holes are anything but black – and we've found more than 75,000 of the brightest ones

  • Written by Jessica Thorne, Astrophysics PhD Candidate, The University of Western Australia
Some black holes are anything but black – and we've found more than 75,000 of the brightest ones

When the most massive stars die, they collapse to form some of the densest objects known in the Universe: black holes. They are the “darkest” objects in the cosmos, as not even light can escape their incredibly strong gravity.

Because of this, it’s impossible to directly image black holes, making them mysterious and quite perplexing. But our new research has road-tested a way to spot some of the most voracious black holes of all, making it easier to find them buried deep in the hearts of distant galaxies.

Despite the name, not all black holes are black. While black holes come in many different sizes, the biggest ones are at the centres of galaxies, and are still growing in size.

These “supermassive” black holes can have the mass of up to a billion Suns. The black hole at the centre of our own Milky Way galaxy – called Sagittarius A*, whose discovery received the 2020 Nobel Prize in Physics – is fairly calm. But that isn’t the case for all supermassive black holes.

If material such as gas, dust or stars gets too close to a black hole, it gets sucked in by the enormous gravitational force. As it falls towards the black hole, it heats up and becomes incredibly bright.

The light produced by these “bright black holes” can span the entire electromagnetic spectrum, from X-rays to radio waves. Another name for the bright black holes at the centre of galaxies is “active galactic nuclei”, or AGN. They can shine trillions of times brighter than the Sun, and can sometimes even outshine all the stars in its galaxy.

Image of black hole
Matter swirling into the supermassive black hole at the centre of M87. Event Horizon Telescope

The brightest black holes

Some AGN violently spew out matter via a jet, which travels millions of kilometres through space and can be seen by radio telescopes. Others produce “winds” at the centre of the galaxy, capable of pushing any gas (the fuel needed for stars to form) out of the galaxy.

Violent jets spewing from Hercules A
Violent jets spewing from Hercules A. NASA/ESA/NRAO

Read more: Like a spinning top: wobbling jets from a black hole that's 'feeding' on a companion star

With such destructive forces in the middle of a galaxy, astronomers are certain this must have a big impact on the galaxy itself. We know most galaxies are slowly turning off their star formation processes, and AGN might be one of the culprits.

AGN can therefore not only help us to better understand elusive black holes, but studying them also teaches us about galaxies themselves.

Finding bright black holes

Depending on how much a black hole is “eating”, what galaxy it’s in, and the angle from which we can see it, AGN can look very different to one another. Even when looking at the same galaxy, one astronomer with an X-ray telescope may see it glow and discover an AGN, whereas another astronomer using a radio telescope might see nothing, if the AGN doesn’t happen to produce jets that are visible in the radio spectrum.

Because of this, it was thought they were all different objects, but by looking at the same objects with different telescopes astronomers discovered they had many similarities, and realised the benefits of using more of the electromagnetic spectrum to find them.

The relative brightness of a galaxy across different parts of the electromagnetic spectrum is called its “spectral energy distribution”. This can be used to measure how many stars are in a galaxy, how old they are, what they’re made of, and how much dust is blocking the light.

Image of galaxy at different wavelengths
Composite picture showing how a typical galaxy appears at different wavelengths. ICRAR/GAMA and ESO

In our research, published today in Monthly Notices of the Royal Astronomical Society, we show that this technique can also be used to spot AGN. This means we can now measure not just the properties and histories of the stars in the galaxy, but also the brightness of its central black hole.

It’s not a simple thing to do. The difference between starlight and the light from an AGN is incredibly subtle, so it’s possible to confuse young stars for a bright black hole, and vice versa.

Here in Australia, astronomers have been using Australian telescopes to make 3D maps of galaxies in specific patches of the sky. These maps let us scour hundreds of thousands of galaxies, spanning 11 billion years of history, for possible AGN.

By applying our new method to 700,000 galaxies we identified and quantified more than 75,000 AGN to begin understanding how their number has evolved over time and how they have impacted their host galaxies. Astronomers think the number of AGN in the Universe is linked to the amount of star formation, which we know was almost ten times higher roughly 10 billion years ago. But until we can be certain we’ve identified all the AGN across cosmic time in our galaxy samples, we won’t know for sure.

Read more: The heaviest stellar black hole in our galaxy is even more massive than we thought

Right now, the astronomical community is still passionately debating the nature of active black holes. While we haven’t yet answered the questions needed to soothe the debate, we’re now one step closer to reliably being able to spot these fascinating objects within galaxies. And that’s an important step towards shedding more light on the mystery of black holes.

Authors: Jessica Thorne, Astrophysics PhD Candidate, The University of Western Australia

Read more https://theconversation.com/some-black-holes-are-anything-but-black-and-weve-found-more-than-75-000-of-the-brightest-ones-169938

7 Common Air Conditioner Issues in Melbourne – And How to Fix Them

Image by freepik Living in Melbourne, we all know how unpredictable the weather can be. One moment it’s cold and windy, the next it’s a scorchin...

Powering Palm QLD with Reliable Electrical Solutions

Image by pvproductions on Freepik When it comes to finding a trustworthy electrician Palm QLD locals can count on, the team at East Coast Sparkies s...

The Smart Way to Grow Online: SEO Management Sydney Businesses Can Rely On

If you’re a Sydney-based business owner, you already know the digital space is crowded. But with the right strategy, you don’t need to shout the...

What Your Car Says About You: The Personality Behind the Vehicle

You can tell a lot about someone by the car they drive—or at least, that’s what people think. True Blue Mobile Mechanics reckon the car says a l...

The Confidence Curve: Why Boudoir Photography Is the Empowerment Trend You Didn’t Know You Needed

Boudoir photography has been quietly taking over social feeds, Pinterest boards, and personal milestones—and for good reason. It’s not just abou...

Understanding Level 2 Electricians: Why Sydney Residents Need Licenced Experts for Complex Electrical Work

When it comes to electrical work around the home or business, not all electricians are created equal. In Sydney, particularly when you're dealing wi...

Retirement Anchored in Model Boat Building for Waterford’s Doug Unsold

WATERFORD — When Doug Unsold sees his ship come in, it’s usually one he’s crafted with his own hands. The 67-year-old retiree from Waterford ...

The Science Behind Alarm Clocks and Your Circadian Rhythm

Waking up on time isn’t just about setting an alarm—it’s about working with your body, not against it. At the heart of every restful night and...

How to Use Plants to Create a Calming Atmosphere in Your Home

In today’s fast-paced world, cultivating a calm, soothing environment at home has never been more important. Whether you live in a busy urban apar...

How Maths Tutoring Can Help Students Master Maths

Mathematics can be a daunting subject for many students, often causing stress and frustration. However, maths tutoring has proven to be an effective...

Refurbished iPads Are Better Than New Ones (Here's Why)

Image by rawpixel.com on Freepik Apple's refurbished iPad program has quietly become one of the best deals in tech. While everyone obsesses over the ...

Your Guide to Finding the Right GP: What Perth City Doctors Offer Today

Choosing a General Practitioner (GP) is one of the most important health decisions you’ll make. Luckily, Perth’s vibrant CBD now hosts a new ge...

Why Every Mining Operation Needs a Robust Safety Management System

Mining is one of the backbones of the Australian economy, particularly in Western Australia. Back in 2019-20, mining contributed 10.4% of Australia...

Australian Classic Literature Enjoys Resurgence

Welcome back to the good old days of storytelling! As the modern world becomes increasingly more demanding, returning to childhood favourites offers...

How to Choose the Right Lawyers in Sydney for Your Situation

When faced with a legal issue, selecting the right legal representation can make all the difference. Whether you're dealing with a personal injury, ...

Building a Governance Model for Headless Content Management at Scale

Image by pch.vector on Freepik There's never been a better time to implement a headless content management system (CMS) to gain the flexibility and ...

Understanding Trade Insurance: Essential Protection for Businesses

Image by Drazen Zigic on Freepik In the current economic environment, trade insurance is an important element for companies trading both locally an...

Choosing the Right Timber for External Cladding

Timber cladding is one of those finishes that pulls double duty: it makes a building look warm and welcoming, and it quietly shields the frame from ...