Our galaxy, the Milky Way, is made up of a hundred billion stars, one of which is our Sun. At the heart of the Milky Way sits a black hole called Sagittarius A*. Just as the Earth is in orbit around the Sun, the Sun is in orbit around Sagittarius A*, albeit with a longer orbital period. It takes the Earth just 365 days to orbit the Sun, whereas it takes the Sun 240 million years (traveling at 800,000 km/h) to orbit Sagittarius A*.
Space is spacious
Until the 1920s, it was believed that the Milky Way was all the Universe had to offer. Then it got a lot bigger when it was discovered that there were, in fact, around a hundred billion galaxies much like the Milky Way. It turns out there’s nothing remarkable about the Milky Way after all.
The Milky Way is the appropriately named milky structure in this image. It’s a spiral galaxy that appears as a band because Earth sits in an arm and we’re looking out through the disk. (Image credit: B. Fugate)
Although most galaxies are too far away to be seen with the naked eye, each galaxy is thought to harbour a hundred billion stars of its own. To reiterate, there are a hundred billion galaxies in the observable Universe and each galaxy has a hundred billion stars. Putting it mildly, there are a lot of stars.
Take a moment to appreciate how many beaches and deserts there are all over the world. It’s true to say that there are more stars in the Universe than there are grains of sand on Earth. (If we turn our attention to look to the smallest scales, we will find that there are more atoms in a single grain of sand than there are stars in the universe — but that’s a discussion for another day.)
A hundred billion galaxies… how can we get a handle on this number? An image known as the Hubble Ultra-Deep Field can provide a little insight. It involved the Hubble Space Telescope pointing at an incredibly small patch of sky — about 0.000008% of the sky, equivalent to the size of a tennis ball at a distance of 100 metres. This was a regular old piece of the night sky, appearing blank to the naked eye. However, the Hubble Space Telescope viewed the tiny area for a few days so as to detect even the faintest galaxies. The result was spectacular: a cosmic zoo of galaxies, with more shapes, sizes, and colours than you could shake a stick at.
Almost all of the ten thousand objects in the Hubble Ultra-Deep Field image are galaxies, each containing hundreds of billions of stars.
Of all the galaxies, in all the universes, you had to walk into mine
At the heart of each galaxy, you’ll find a supermassive black hole and there is one such black hole that is of particular interest to me at the moment. It’s perched at the nucleus of a galaxy over twenty billion trillion kilometres away and goes by the name of 3C 273 — admittedly, not the catchiest of names but it is practical. It comes from the fact that, in the Third Cambridge Catalogue of Radio Sources (“3C”), it was the 273rd source identified (“273”). For the sake of this post though, let’s call him Bill.
Bill is an active galaxy, giving off a lot of light — not just visible light, but also radio waves, microwaves, infrared light, ultraviolet light, x-rays, gamma-rays… you name it, he’s dishing it out left, right, and centre. These types of light are differentiated by the length of the light waves (with radio waves being the longest waves and gamma-rays being the shortest).
Specifically, I’m studying the radio emission from Bill. Even though light travels at over a billion kilometres an hour, it still takes the radio waves over two billion years to reach Earth because Bill’s so far away. This means that the radio waves we receive today were emitted by Bill over two billion years ago. We are seeing how he looked in the past. If Bill died today (for instance, if all of the stars in the galaxy stopped shining), we wouldn’t know about it for another two billion years… assuming we’re still knocking about then.
The distance to Bill helped cement his place in history. When he was discovered in 1963, people thought he was a star, and that was the end of it. Then they measured the distance to him and found he was really far away — way beyond the outer limits of our galaxy. The implication was that if he was that far away, then he couldn’t be a star. They had to change his classification from “stellar object” to something else. A new category was made — “quasi-stellar objects” — and this was later shortened to quasar. Many quasars have been discovered since then. Bill had a role to play during the 20th century in helping humanity come to terms with what lays beyond our galaxy.
Here’s an analogy. Let’s say you’re a child in a playground. You’ve a few Crayola to hand and decided you’ll make a map of the playground, including everything in it: the slide, the swing, the sandpit, the second slide, etc. You want to know how far away they are so you can map the location of everything accurately. So you’re walking around, getting down to business, and realise that the one of the slides actually isn’t in this playground at all. It’s across the street in another playground! Mind blown. You thought that the playground you were in was the only one in the world! Secondly, the slide that’s across the street must be huge because it’s easily spotted from here. You take a closer look and it turns out to be a super slide made up of a few different smaller slides. Now it isn’t really right to call this a slide because it’s very different from the slide we already know and love, so we change the name of it to a “quasi-slide object” — kind of like a slide but not quite. This is what happened with black hole Bill. We thought the galaxy was just a star in the Milky Way because it was so bright but it turned out to be a different galaxy altogether because of how far away it was.
So what is he at these days? Bill is accreting matter from a disk and firing off a jet of super fast and energetic plasma (as you do). The jet is huge, extending two billion billion kilometres in length (think the distance between the Earth and the Moon times a trillion). My goal is to try to understand what’s going on there.
This is an artist’s impression of an active galaxy like 3C 273. The black hole is (paradoxically) within the bright nucleus. The region appears bright because the black hole is tearing up stars, causing lots of friction. This heats up the material, making it shine. There’s a pretty simulation showing a black hole destroy a star which ventured too close to its event horizon. The black hole itself does actually appear black.
Bill’s jet is made of electrons, one of the fundamental building blocks of the Universe. To explain what we see in the jet, we have to figure out what the electrons are doing. That is, to understand how this astronomically big structure works, we have to describe the activities of electrons which measure just 2.8 quadrillionths of a metre. There is something neat about having to go to these small scales in order to be able to interpret the large-scale motion. (Strictly speaking, it’s incorrect to think of the electron as having a size. They have no spatial extent. Electrons also do lots of other mad things because of quantum mechanical effects, like being in multiple places simultaneously, but that’s a tale for another time.)
This is a real image of Bill taken by the Hubble Space Telescope. The black hole is located at the centre of the bright source. The large-scale jet that’s being emitted from the core can be seen in the top left of the picture.
The instrument of choice
I use a very sensitive radio telescope called LOFAR to observe Bill because he gives off extremely faint radio waves. For context, let’s say you were chilling out on the Moon for the laugh, and in the hustle and bustle of making the last rocket of the night back to Earth, you left your iPhone 5S in a crater. Well the radio waves given off by the mobile phone on the Moon would be about a hundred times brighter than Bill.
We’re also able to study features in this jet with outstanding resolution. Take a hair and write your name on it. Place is ten metres away from you. With the resolution of the LOFAR telescope, we could read what it says.
The LOFAR station located in Co. Offaly. It forms part of an international telescope. (Credit: I-LOFAR)
Show me the money
What do we hope to learn about black holes from studying Bill? Well, we want to know how and why they work. I’m often asked of what use this is to anyone but it’s useful for just that — understanding how black holes like Bill work. It might seem like circular reasoning but understanding how the Universe operates is a sufficient reason in and of itself to do the research
What was once blue sky research led to many indispensable technologies such as the Internet and computers. You never know when the next breakthrough is coming and what its implications will be for society. Astrophysics is often at the edge of this frontier as there is no immediately obvious application but you never know when it’ll pay dividends.
The link between a massive object two billion light years away and an everyday application might seem tenuous, but think of the Universe as a game of chess where the laws of physics are the rules. If we learn how a rook moves on one side of the board, those same restrictions apply throughout. So if we learn something new about how matter behaves out in Bill’s neck of the woods, the stuff here on Earth must obey the same laws.
The other nice feature of the universality of these laws is the fact that, even in the event that humanity was obliterated and a new intelligent species came to dominate, they too would discover exactly the same laws as we use. In fact, other intelligent civilisations in the Universe would also have their own Einstein to discover relativity because it works the same everywhere. The physical laws were here before us and they’ll be here after us. They’re one of the most objective, independent lines of enquiry we can follow. (We’re rubbing up against a classic problem in philosophy here: Do numbers exist?)
As a species, knowledge is all we have. All that separates a pile of silicon, copper, and a few other elements from being organised into an iPhone is an understanding of how to arrange the atoms. The technological exploits of humanity in the year 3000 BC and 3000 AD is partitioned only by knowledge and expertise. Information alone prevented the archetypal cavemen from putting his brethren on the Moon. It’s therefore in our interest as a species to invest heavily in acquiring knowledge and applying our collective intelligence as best we can, to carve out the future we desire — one with an abundance of meaning and absence of suffering for all who inhabit it.
Finally, note that astronomy isn’t a difficult field to advance, given the requisite technology. For example, the laws of physics, insofar as we understand them, are remarkably well behaved. The only way our phones work is because we can make very accurate predictions about many different things with near bang-on certainty. On the other hand, the most complex object in the known Universe is sitting in our skulls. This makes it very difficult to predict people’s thoughts and behaviours precisely and accurately. Topics like social science and psychology are inherently messy, data is difficult to parse, and results are challenging to reproduce. Studying astrophysical phenomena is easier in this regard — a jet from a black hole makes no conscious decisions. The fact of the matter is, we can make predictions about things such as black holes far better than we can say anything about people.
It might be easier to make progress, but I’ll grant that astrophysics is tough to study because of the inaccessible nomenclature and tricky mathematics to boot. However, as my main man JFK put it, we do things “not because they are easy, but because they are hard.”