Read about the coolest discoveries, research updates, and images of this week’s astronomy: New insights into turbulence raging inside distant stars, a discovery of one of the largest black hole jets, and a beautiful image of a comsic dance!
New insights into turbulence raging inside distant stars
Stunning new images created by Keele researchers highlight the turbulent flow of energy inside distant stars.
They were created using the 3D simulation software “PROMPI”, which scientists have been using to investigate stellar interiors with the aim of understanding the science of stellar evolution and black holes.
For years scientists have used one-dimensional models to explain and understand how stars are structured and how they evolve over time. But these models are often limited in how well they can explain the structure of stars, as they take a very general view of the entire star rather than offering any detailed analysis.
But new research led by is helping to make these models more accurate, using 3D hydrodynamic simulations to look at the star’s layers and chemical composition in much greater detail than has previously been possible.
Much like planets, stars have multiple layers, and for this study published in Monthly Notices of the Royal Astronomical Society, the researchers used existing data from previous 1D simulations and focused on a small section of the star in minute detail—in this case, a layer known as the neon-burning shell.
They conducted hydrodynamic simulations using the available data and looked at how fluids move about within the layer they are confined to, and how they drag along some material from the neighboring layers—a process known as entrainment, as well as how these chemicals move between the layer’s borders, known as convective boundaries.
These simulations offer an unprecedented degree of realism in recreating the environment within a star, but more importantly, they also highlight the limitations of the current 1D models. These findings therefore have a huge role to play in helping us improve the accuracy of these models, which in turn will help us understand how astronomical phenomena are structured, such as black holes, supernovae, and neutron stars.
If you want to read more, the full paper is hosted on arxiv: https://arxiv.org/pdf/2207.03223.pdf
A discovery of one of the largest black hole jets
Astronomers have discovered one of the biggest black hole jets in the sky. Spanning more than a million light years from end to end, the jet shoots away from a black hole with enormous energy, and at almost the speed of light. But in the vast expanses of space between galaxies, it doesn’t always get its own way.
This process is analogous to an effect seen in jet engines. As the exhaust plume blasts through the atmosphere, it is pushed from the sides by the ambient pressure. This causes the jet to expand and contract, pulsing as it travels. As the image below shows, we see regular bright spots in the jet, known as “shock diamonds” because of their shape. As the flow compresses, it glows more brightly.
As well as in jet engines, shock diamonds have been seen in smaller, galaxy-sized jets. We’ve seen jets slam into dense clouds of gas, lighting them up as they bore through. But jets being constricted from the sides is a more subtle effect, making it harder to observe. However, until NGC2663, we’ve not seen this effect on such enormous scales.
This tells us there is enough matter in the intergalactic space around NGC2663 to push against the sides of the jet. In turn, the jet heats and pressurizes the matter. This is a feedback loop: intergalactic matter feeds into a galaxy, galaxy makes black hole, black hole launches jet, jet slows supply of intergalactic matter into galaxies. These jets affect how gas forms into galaxies as the universe evolves. It’s exciting to see such a direct illustration of this interaction.
A preprint of the paper is visable here: https://arxiv.org/pdf/2207.06713.pdf
A spectacular cosmic dance
ESO’s Very Large Telescope (VLT) has imaged the result of a spectacular cosmic collision—the galaxy NGC 7727. This giant was born from the merger of two galaxies, an event that started around a billion years ago. At its center lies the closest pair of supermassive black holes ever found, two objects that are destined to coalesce into an even more massive black hole.
Just as you may bump into someone on a busy street, galaxies too can bump into each other. But while galactic interactions are much more violent than a bump on a busy street, individual stars don’t generally collide since, compared to their sizes, the distances between them are very large. Rather, the galaxies dance around each other, with gravity creating tidal forces that dramatically change the look of the two dance partners. “Tails” of stars, gas and dust are spun around the galaxies as they eventually form a new, merged galaxy, resulting in the disordered and beautifully asymmetrical shape that we see in NGC 7727.
The consequences of this cosmic bump are spectacularly evident in this image of the galaxy, taken with the FOcal Reducer and low dispersion Spectrograph 2 (FORS2) instrument at ESO’s VLT. While the galaxy was previously captured by another ESO telescope, this new image shows more intricate details both within the main body of the galaxy and in the faint tails around it.
In this ESO VLT image we see the tangled trails created as the two galaxies merged, stripping stars and dust from each other to create the spectacular long arms embracing NGC 7727. Parts of these arms are dotted with stars, which appear as bright blue-purplish spots in this image.
Also visible in this image are two bright points at the center of the galaxy, another telltale sign of its dramatic past. The core of NGC 7727 still consists of the original two galactic cores, each hosting a supermassive black hole. Located about 89 million light-years away from Earth, in the constellation of Aquarius, this is the closest pair of supermassive black holes to us.
The black holes in NGC 7727 are observed to be just 1600 light-years apart in the sky and are expected to merge within 250 million years, the blink of an eye in astronomical time. When the black holes merge they will create an even more massive black hole.
The search for similarly hidden supermassive black hole pairs is expected to make a great leap forward with ESO’s upcoming Extremely Large Telescope (ELT), set to start operating later this decade in Chile’s Atacama Desert. With the ELT, we can expect many more of these discoveries at the centers of galaxies.