Supermassive galaxy mystery Definitely Maybe solved

Two rather cool things have happened this week, so I've tried to squeeze them both into one title. In no particular order, a mystery that has been bothering astronomers for the last year has seemingly come to an anticlimactic conclusion, because it turns out there probably wasn't really a mystery at all. Secondly, arguably the biggest and best British rock band has just announced a historic reunion! Oasis returns and the Gallagher brothers will be back sharing a stage to the joy of countless fans once more. The curious wording of the article title is because their debut studio album was called Definitely Maybe, and yes I am well aware that was released almost a decade before I was born. But back to the astronomy for now.

The most powerful telescope to date, the JWST, started sending back cosmic snaps just over two years ago, and its early images were causing some surprise and confusion among astronomers. The telescope can detect light from some of the earliest galaxies in the Universe, and astronomers peering at these images expected to find tiny, low mass, unevolved, infant galaxies. Instead, the galaxies appeared enormous, being so massive and having grown so quickly that were completely in contradiction to computer simulations modelling their evolution. Perhaps that suggested that our understanding of the Universe, the big bang and the standard model of cosmology was flawed, or incomplete, given that observations seemed to show galaxies far more massive than models predicted they should have been. It was all getting rather interesting, and I was beginning to wonder whether our physics textbooks and lectures would have to be rewritten... but a new study seems to suggest that these galaxies aren't supermassive after all, and that our cosmological models seem to be holding up for now. So what exactly happened? It turns out black holes may have played a part.

Image credit: NASA, ESA, CSA, Steve Finkelstein (UT Austin)

Thousands of galaxies cover this image of the CEERS survey by the JWST. Some of them are so distant their light has been travelling for 13 billion years, harking back to the very beginning of the Universe.

Black holes are astronomical objects with a gravitational pull so strong that nothing, not even light, can escape them. Matter and light fall in and can never get out. These mind boggling objects dwell in the hearts of most large galaxies. While black holes cannot be seen directly (because they're dark and so is space), they can be observed indirectly. The biggest black holes can weigh up to billions of times more than our sun. Exactly where these supermassive black holes come from is not fully understood, but we do know they exist from the earliest days of a galaxy's life. Black holes can grow by accreting (that's astronomer lingo for accumulating) nearby matter that falls into them, such as gas stripped from neighbouring stars, and even other black holes. When a black hole feeds on nearby material, jets of particles and light are blasted out from the its poles at enormous speeds and are so long they can be detected by telescopes. The surrounding bright light, as in the photo below, is caused by hot plasma in a disc of swirling matter which accelerates inwards, getting so hot from friction that it releases heat as light radiation. The event horizon is the radius around the black hole which, after entering, nothing can escape. Outside the event horizon, light is emitted from hot plasma and bends around the black hole to make a curved ring of light. An example of this is seen below, and hopefully provides a clearer understanding as to why black holes, while not emitting light, can make it seem like galaxies are brighter than they really are.

Image credit: Event Horizon Telescope Collaboration

Above is the first ever image of a black hole, which lies at the centre of a galaxy called M87. The bright ring formed around it is due to photons of light bending in the intense gravity around this black hole, which weighs a hefty 6.5 billion times more than the sun. Image released in 2019.

This latest paper suggests that the galaxies which appeared overly massive likely host black holes rapidly consuming surrounding gas. Friction of the fast moving gas which gets sucked into the black hole emits heat and light, making the galaxies appear much brighter than if their light was only from their resident stars. This extra light from the disc around the black hole makes galaxies appear like they have more stars, and brighter stars, than they really do, which in turn gives the impression that these galaxies are more massive than they really are. When these particular galaxies are removed from the JWST images, the remaining early galaxies do indeed fit within the predictions of current models. It isn't all as expected however, since there are roughly twice as many massive galaxies in the JWST's data than predicted by the standard model. Possibly, stars formed more quickly in the early Universe than they do now. This is a spot of good news for me at least since I find star formation very interesting, and also the photos of it are absolutely stunning, as can be seen in my previous articles, and also in this new JWST image released only this week. The next article will feature that image, because not only is it gorgeous, it is also a site of a brand new discovery...

And on that astronomical cliffhanger, time to change tack entirely with a new subject. Concerts I go to tend to involve violins and choirs, since I happily participated in both at school, with performances in nearby churches. Last year a fellow astrophysicist and I tried something different and went to watch Noel Gallagher singing live, which was rather good fun. I always like playing the songs of either Oasis or the individual Gallaghers in my car when I've got the roof down on a sunny day, luckily a lot of other people like their music too so they don't tend to mind the free concert at the traffic lights. I'm aiming to get a sportscar/convertibles article out soon, but lots of exciting astrophysics news keeps popping up so we shall see what gets published first! In the meantime, here is a photo from the very orderly and civilised rock concert we saw by Mr Gallagher Snr last year. Happy days!

Noel Gallagher singing live in November 2023, which my fellow astrophysicist and I thoroughly enjoyed.