May 2024 : Galaxy evolution: not so sim(ple)ulations

Episode Audio

Galaxy evolution: not so sim(ple)ulations. This month, Kammy and Jessy are joined by Dr. Ana Duarte Cabral from Cardiff University, where she discusses her work on understanding the connection between star formation and galaxy evolution and clues us in on how simulating these processes are not a simple affair. Fiona and Phoebe report on the recent discovery of a quiet Galactic black hole, and observations of a loud white dwarf star. Ask an Astronomer makes a return with George and Honor!

The News

New black hole discovered by Gaia

The Gaia collaboration has recently announced the discovery of a new black hole in the Milky Way which belongs to a very rare population. This black hole, dubbed Gaia BH3, is a quiescent black hole, meaning that it isn’t currently accreting material from its companion star and hence isn’t emitting any light. Thus, it is functionally invisible to our telescopes. Only three quiescent black holes have been spotted so far - all discovered by Gaia - because detecting them relies on spotting the gravitational wobble they cause in the orbit of a binary companion star. Gaia BH3’s companion has an orbital period of around 11.6 years, so it takes a considerable amount of observation time to definitively identify the presence of a hidden black hole companion.

In addition to being the third quiescent black hole ever discovered, Gaia BH3 has a number of other interesting characteristics. It’s the second closest black hole to the Earth that we know of, at a distance of around 19,000 light years from us, and it’s also the most massive stellar black hole - a black hole formed by a single star rather than a merger event - that we’ve ever observed, at 33 times the mass of the Sun. This population of black holes has been detected via gravitational wave observations, but sources with this mass are very rarely seen directly; only one other black hole with a mass above 10 solar masses has been observed thus far, so having a second example to study is very useful when trying to understand how these black holes form.

Gaia BH3 is also a metal-poor black hole and hence dates from the earliest phases of star formation in the Milky Way at an estimated 11 billion years old, but - for an additional surprise - its orbital motion indicates it may not have originated in the Milky Way itself, instead hailing from a nearby galaxy or globular cluster which merged with our Galaxy some time in the distant past. With so many unusual characteristics in one object, this black hole has a lot of promise for study, and with another five years planned for the Gaia mission, we can hope that there’ll be yet more interesting discoveries like this one to come.

Dramatic brightening of a white dwarf star

Between now and this September a star, T Coronae Borealis, which is currently invisible to the naked eye, will become visible for a short while during a nova event. The star is part of a binary system in the constellation Corona Borealis and it is currently at a magnitude of 10. During the nova event, the star is expected to temporarily increase its magnitude to 2, bringing it to about the same brightness as the stars in the Plough constellation. Remember, magnitudes are like golf scores - lower means bigger!

The star undergoing this brightening is a white dwarf. White dwarfs are incredibly dense, but are not normally very bright. However, this one is in a binary system with a red giant star. As the red giant star’s temperature increases, its outer layers expand, pushing extra stellar material close to the white dwarf. The white dwarf then accretes this material and heats up, thus increasing its brightness. The white dwarf will then gradually cool again over the next few weeks and the star becomes invisible once again.

Interview with Dr. Ana Duarte Cabral

Kammy and Jessy talk with Dr. Ana Duarte Cabral, a Royal Society University Research Fellow at Cardiff University, about her research interests and about being an academic in astronomy. We discuss the interconnectivity between star formation and galaxy evolution, and how approaching the problem from both observational and theoretical angles can yield the best results. She talks about the differences between the two fields of observations and simulations, and the challenges in marrying together small-scale stellar core astrophysics, with large-scale Galactic mechanics. We also hear a little about what it's like becoming a PhD supervisor for the first time, and about the work of Ana's research group, which includes her two PhD students and her postdoctoral researcher.

Odds and Ends

This month we’re reading and discussing the paper Purple is the new green: biopigments and spectra of Earth-like purple worlds, published by Monthly Notices of the Royal Astronomical Society.

As the number of Earth-like exoplanets we’ve detected increases, the hunt is on for potential signs of microbial life on those planets. This paper suggests that rather than the leafy greens we see on Earth, we might just want to be keeping an eye out for something purple! While bacteria which use green chlorophyll to help them photosynthesise are responsible for the oxygen-rich environment of modern Earth, they were preceded by a number of purple bacteria species which produce an entirely different set of pigments. To detect these sorts of bacteria on exoplanets, we need to understand how these pigments might affect the way such a planet might reflect light.

In this paper, scientists at Cornell University and the University of Minnesota cultured a number of different species of purple bacteria to determine how they’d appear on the surface of a planet. Despite being called purple bacteria, they often produce a set of pigments called carotenoids, which are responsible for the red and orange hues in a number of vegetables on Earth - including carrots! - and the cultures show an array of red-toned pigments very different to the environment on Earth. After determining how these pigments reflect light, these astronomers used the results to model a number of different Earth-like planets populated by purple bacteria which can now be used as templates for what to expect if we happen to spot one in reality.

As part of this study, the authors also discussed the environments in which these bacteria might thrive. Purple bacteria still exist on Earth, and can be seen in one potentially unexpected environment - because they’re capable of using infrared light to produce energy for themselves when there’s no visible light, they thrive in places like deep-sea vents. The fact they can do this means that they might be particularly well-suited to survival on planets with a star which is a lot redder than our own Sun, such as M-type stars, the coolest and reddest stars on the stellar main sequence.

This paper highlights that while it’s tempting to look for life as we know it to exist on Earth, photosynthetic bacteria are actually a relative newcomer, having only appeared within the last 1.2 billion years. If we want to look systematically, we need to consider other possibilities - including that other planets might just be purple.

Ask and Astronomer

We’re bringing back Ask an Astronomer, and this time George Bendo and Honor Harris answer a question we received at Bluedot 2023.

Q: What would happen if a black hole came near our planet?
A: If the Sun turned into a black hole for example, the difference we could notice would be in the lack of sunlight coming to Earth. In terms of our orbit, nothing would change for any of the planets in the system. However, if an object of significant mass such as a star or black hole were to enter the solar system, and move through it then that would definitely disrupt the orbit of the planets including Earth, likely throwing them out of the solar system and on different pathways.

Q: Does the Lovell Telescope link up with other telescopes collectively when producing results?
A: The Lovell Telescope is part of eMERLIN, which is a network of seven radio antennas spread across the United Kingdom that can function as one telescope. Additionally, the Lovell Telescope can function as part of the European VLBI (Very Long Baseline Interferometry) Network, where it works along with other radio antennas across Europe as one much larger telescope. The multiple telescopes working together have more collecting area than just one antenna by itself, allowing them to see fainter things than an individual telescope. In addition, multiple radio antennas spread over a larger area can produce sharper images than just a single dish working by itself.
When the Lovell does this, the astronomers do not just measure the signals from the individual antennas. Instead, astronomers measure the signals from pairs of antennas. When the signals are combined, the wave patterns will either add together or cancel out, thus producing interference patterns (which is why astronomers will refer to things like e-MERLIN as an interferometer). Mathematical analyses can then be used to take the amplitudes and phases from the pairs of antennas and transform that back into an image.

Q: Would we have to live underground on Mars?
A: Mars has an atmosphere that is over 100 times thinner than the atmosphere we have on Earth, and therefore whilst there is still some protection from the Sun’s radiation, if we stood on the surface of Mars with no protection the radiation would kill us humans over only a couple of months. This is because Mars experiences 40-50 times more natural radiation than Earth, which is also due to its lack of magnetosphere. Whilst we could build a base on the surface with similar materials to that used in spaceships which can block radiation, going underground would also provide that sort of protection as dirt and rock are very good at blocking radiation.
Furthermore, there is the temperature to consider - on the surface of Mars the temperature can range from 20 degrees celsius to -153 degrees celsius as the heat from the Sun easily escapes through the thin atmosphere. Ultimately, if we were going to live on Mars, we would require a complex or base either on the surface or underground. Building an underground base is a hard process and requires digging and time to do that, however it does provide benefits you don’t always get from a surface base, such as greater protection from the lethal blasts of solar flares that occasionally occur. For this reason I could imagine that if we were to live on Mars we would probably have a combination of a surface and underground base in order to survive on the red planet.


Here is some feedback we have received over the past month via our email address. Please keep your comments coming!

Christina Smith (former Jodcaster)
Just wanted to share that it's lovely to see and hear the Jodcast again!

T. K. Arispe
First off, the new website looks really nice! I'm so glad the Jodcast is back. You were sorely missed.
I was poking around the new website layout, and I noticed that in the archive of back episodes available from the main page, the oldest listed episode is March 2014. Will you ever make the older episodes accessible again? My mom and I have been listening through the back episodes sequentially, and we're only in 2011; I'd hate to have to skip a few years of delicious astrophysics goodness.
Jod on!

In Memoriam

Finally, we’re going to have to end this episode with some unhappy news. We’re deeply saddened to say that Prof. Ian Morison, a long-time contributor to the Jodcast, has recently passed away at the age of eighty after a long illness.

Ian began working at Jodrell Bank in 1965 as a research student, taking on a permanent post in 1970, and had a hand in working on a number of radio telescopes during his time there, including the iconic Lovell telescope, and played a key role in the development of the MERLIN radio interferometer network.

While Ian’s research had a focus in the radio, he had been a keen optical astronomer from a young age, and it’s in this context most will have known him on the Jodcast - a soothing voice telling you about all you could see in the night sky in the month ahead, with an assortment of helpful tips about how to make the most of it for amateur astronomers and astrophotographers.

As well as this, he contributed his knowledge and passion for astronomy via a diverse array of publications and events. Ian was a familiar face giving talks at a number of astronomy societies, including at the Macclesfield Astronomy Society, which he helped to found. Given this love of science communication it’s no wonder that he was awarded the prestigious position of Gresham Professor of Astronomy, a role dating back to the 16th century which was created for the purpose of providing free, educational lectures to the public. He produced a series of 25 hour-long lectures on astronomy during his tenure, all of which are accessible online.

If any of our listeners have fond memories of Ian from the Jodcast or elsewhere, we’d welcome you sharing them. If anyone wishes to make a donation in his memory, his family have requested that it should go to East Cheshire Hospice. From all of us here, our thoughts are with Ian’s family and friends, and he’ll be remembered fondly and missed by us all.

Show Credits

Interview : Dr. Ana Duarte Cabral and Kammy Bogue, Jessy Marin
Presenters : Fiona Porter and Phoebe Ryder
Editors : George Bendo, Louisa Mason and Jessy Marin
Website : Lily Correa Magnus & James Turner
Producers : James Turner and Lily Correa Magnus
Cover Art : A still from an AREPO simulation of gas in an evolving galaxy's temperature and density. CREDIT: Springel, V. (2010) & Harvard-Smithsonian Center for Astrophysics.