Thu 12 Jun 16:00: Transient astrophysics with the Gravitational wave Optical Transient Observer (GOTO)
Gravitational-wave (GW) multi-messenger astronomy holds immense promise for our understanding of the Universe, impacting studies of cosmology, the production of elements, and the final fates of stars. To date, however, only a single credible source, GW170817 , caused by the merger of two neutron stars, has been detected both in GWs and electromagnetically. I will discuss the scientific potential and challenges of observing more multi-messenger events, as motivation for the GOTO project: a UK-led transient sky survey composed of a fleet of rapidly-responding telescope arrays. The primary science driver of GOTO is scanning the sky in response to GW alerts, to search for their electromagnetic counterparts. Alongside overviewing GOTO ’s capabilities and recent multi-messenger efforts, I will present highlights from various ancillary science enabled by the array. This includes rapid localisation and characterisation of gamma-ray bursts, and discoveries of infant and extreme supernovae beyond the traditional core-collapse and thermonuclear regimes. I will also present our efforts to automate and expedite the characterisation of transients via algorithmically scheduled follow-up and citizen scientists.
- Speaker: Joseph Lyman, University of Warwick
- Thursday 12 June 2025, 16:00-17:00
- Venue: Hoyle Lecture Theatre, Institute of Astronomy.
- Series: Institute of Astronomy Colloquia; organiser: Matthew Grayling.
Apocalypse When? Hubble Casts Doubt on Certainty of Galactic Collision
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NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and B. Whitmore (STScI)
As far back as 1912, astronomers realized that the Andromeda galaxy — then thought to be only a nebula — was headed our way. A century later, astronomers using NASA’s Hubble Space Telescope were able to measure the sideways motion of Andromeda and found it was so negligible that an eventual head-on collision with the Milky Way seemed almost certain.
A smashup between our own galaxy and Andromeda would trigger a firestorm of star birth, supernovae, and maybe toss our Sun into a different orbit. Simulations had suggested it was as inevitable as, in the words of Benjamin Franklin, “death and taxes.”
But now a new study using data from Hubble and the European Space Agency’s (ESA) Gaia space telescope says “not so fast.” Researchers combining observations from the two space observatories re-examined the long-held prediction of a Milky Way – Andromeda collision, and found it is far less inevitable than astronomers had previously suspected.
“We have the most comprehensive study of this problem today that actually folds in all the observational uncertainties,” said Till Sawala, astronomer at the University of Helsinki in Finland and lead author of the study, which appears today in the journal Nature Astronomy.
His team includes researchers at Durham University, United Kingdom; the University of Toulouse, France; and the University of Western Australia. They found that there is approximately a 50-50 chance of the two galaxies colliding within the next 10 billion years. They based this conclusion on computer simulations using the latest observational data.
These galaxy images illustrate three possible encounter scenarios between our Milky Way and the neighboring Andromeda galaxy. Top left: Galaxies M81 and M82. Top right: NGC 6786, a pair of interacting galaxies. Bottom: NGC 520, two merging galaxies. Science: NASA, ESA, STScI, DSS, Till Sawala (University of Helsinki); Image Processing: Joseph DePasquale (STScI)Sawala emphasized that predicting the long-term future of galaxy interactions is highly uncertain, but the new findings challenge the previous consensus and suggest the fate of the Milky Way remains an open question.
“Even using the latest and most precise observational data available, the future of the Local Group of several dozen galaxies is uncertain. Intriguingly, we find an almost equal probability for the widely publicized merger scenario, or, conversely, an alternative one where the Milky Way and Andromeda survive unscathed,” said Sawala.
The collision of the two galaxies had seemed much more likely in 2012, when astronomers Roeland van der Marel and Tony Sohn of the Space Telescope Science Institute in Baltimore, Maryland published a detailed analysis of Hubble observations over a five-to-seven-year period, indicating a direct impact in no more than 5 billion years.
“It’s somewhat ironic that, despite the addition of more precise Hubble data taken in recent years, we are now less certain about the outcome of a potential collision. That’s because of the more complex analysis and because we consider a more complete system. But the only way to get to a new prediction about the eventual fate of the Milky Way will be with even better data,” said Sawala.
100,000 Crash-Dummy SimulationsAstronomers considered 22 different variables that could affect the potential collision between our galaxy and our neighbor, and ran 100,000 simulations called Monte Carlo simulations stretching to 10 billion years into the future.
“Because there are so many variables that each have their errors, that accumulates to rather large uncertainty about the outcome, leading to the conclusion that the chance of a direct collision is only 50% within the next 10 billion years,” said Sawala.
“The Milky Way and Andromeda alone would remain in the same plane as they orbit each other, but this doesn’t mean they need to crash. They could still go past each other,” said Sawala.
Researchers also considered the effects of the orbits of Andromeda’s large satellite galaxy, M33, and a satellite galaxy of the Milky Way called the Large Magellanic Cloud (LMC).
“The extra mass of Andromeda’s satellite galaxy M33 pulls the Milky Way a little bit more towards it. However, we also show that the LMC pulls the Milky Way off the orbital plane and away from Andromeda. It doesn’t mean that the LMC will save us from that merger, but it makes it a bit less likely,” said Sawala.
In about half of the simulations, the two main galaxies fly past each other separated by around half a million light-years or less (five times the Milky Way’s diameter). They move outward but then come back and eventually merge in the far future. The gradual decay of the orbit is caused by a process called dynamical friction between the vast dark-matter halos that surround each galaxy at the beginning.
In most of the other cases, the galaxies don’t even come close enough for dynamical friction to work effectively. In this case, the two galaxies can continue their orbital waltz for a very long time.
The new result also still leaves a small chance of around 2% for a head-on collision between the galaxies in only 4 to 5 billion years. Considering that the warming Sun makes Earth uninhabitable in roughly 1 billion years, and the Sun itself will likely burn out in 5 billion years, a collision with Andromeda is the least of our cosmic worries.
The Hubble Space Telescope has been operating for over three decades and continues to make ground-breaking discoveries that shape our fundamental understanding of the universe. Hubble is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope and mission operations. Lockheed Martin Space, based in Denver, also supports mission operations at Goddard. The Space Telescope Science Institute in Baltimore, which is operated by the Association of Universities for Research in Astronomy, conducts Hubble science operations for NASA.
Explore MoreHubble Provides Bird’s-Eye View of Andromeda Galaxy’s Ecosystem (2025)
Hubble Shows Milky Way is Destined for Head-on Collision with Andromeda Galaxy (2012)
Galaxy Details and Mergers
Hubble Traces Hidden History of Andromeda Galaxy (2025)
Hubble’s High-Definition Panoramic View of the Andromeda Galaxy (2015)
Facebook logo @NASAHubble @NASAHubble Instagram logo @NASAHubble Related Images & Videos Milky Way and Andromeda Encounters
This selection of images of external galaxies illustrates three encounter scenarios between our Milky Way and the neighboring Andromeda galaxy. Top left: Galaxies M81 and M82. Top right: NGC 6786, a pair of interacting galaxies. Bottom: NGC 520, two merging galaxies.
Contact Media
Claire Andreoli
NASA’s Goddard Space Flight Center
Greenbelt, Maryland
claire.andreoli@nasa.gov
Ray Villard
Space Telescope Science Institute
Baltimore, Maryland
- Hubble Space Telescope
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- Astrophysics Division
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A Star Like No Other
An unusual star (circled in white at right) behaving like no other seen before and its surroundings are featured in this composite image released on May 28, 2025. A team of astronomers combined data from NASA’s Chandra X-ray Observatory and the Square Kilometer Array Pathfinder (ASKAP) radio telescope on Wajarri Country in Australia to study the discovered object, known as ASKAP J1832−0911 (ASKAP J1832 for short).
ASKAP J1832 belongs to a class of objects called “long period radio transients” discovered in 2022 that vary in radio wave intensity in a regular way over tens of minutes. This is thousands of times longer than the length of the repeated variations seen in pulsars, which are rapidly spinning neutron stars that have repeated variations multiple times a second. ASKAP J1832 cycles in radio wave intensity every 44 minutes, placing it into this category of long period radio transients. Using Chandra, the team discovered that ASKAP J1832 is also regularly varying in X-rays every 44 minutes. This is the first time that such an X-ray signal has been found in a long period radio transient.
Image credit: X-ray: NASA/CXC/ICRAR, Curtin Univ./Z. Wang et al.; Infrared: NASA/JPL/CalTech/IPAC; Radio: SARAO/MeerKAT; Image processing: NASA/CXC/SAO/N. Wolk
Thu 05 Jun 16:00: The Formation and Co-Evolution of Galaxies and Supermassive Black Holes
Cosmological hydrodynamical simulations are becoming increasingly realistic by incorporating a wider range of physical processes, higher spatial resolution, and larger statistical samples. Despite ongoing trade-offs between resolution and volume, recent advances now allow for simulations that resolve the multiphase interstellar medium and capture the clumpy nature of star formation in galaxies. In this context, I will present how such simulations shed light on the coupled evolution of galaxies and their central supermassive black holes. At high redshift, galaxies tend to be gas-rich, turbulent, and star-bursting, often exhibiting irregular, compact, and disturbed morphologies. As internal turbulence subsides, many systems transition into stable, rotating disc galaxies, typically once they reach stellar masses around 1e10 Msun. Simultaneously, black hole growth is tightly linked to the dynamical state of the host galaxy. In low-mass, turbulent systems, stellar feedback can suppress nuclear gas inflows, delaying black hole growth. Only when galaxies become sufficiently massive and dynamically settled can gas efficiently reach galactic centers to fuel sustained accretion. These processes also have important implications for the spin evolution of black holes or how fast they coalesce, which can reflect the varying modes of accretion and feedback across cosmic time.
- Speaker: Yohan Dubois (Institut d’Astrophysique de Paris)
- Thursday 05 June 2025, 16:00-17:00
- Venue: Hoyle Lecture Theatre, Institute of Astronomy.
- Series: Institute of Astronomy Colloquia; organiser: Matthew Grayling.
Thu 05 Jun 16:00: The Formation and Co-Evolution of Galaxies and Supermassive Black Holes
Cosmological hydrodynamical simulations are becoming increasingly realistic by incorporating a wider range of physical processes, higher spatial resolution, and larger statistical samples. Despite ongoing trade-offs between resolution and volume, recent advances now allow for simulations that resolve the multiphase interstellar medium and capture the clumpy nature of star formation in galaxies. In this context, I will present how such simulations shed light on the coupled evolution of galaxies and their central supermassive black holes. At high redshift, galaxies tend to be gas-rich, turbulent, and star-bursting, often exhibiting irregular, compact, and disturbed morphologies. As internal turbulence subsides, many systems transition into stable, rotating disc galaxies, typically once they reach stellar masses around 1e10 Msun. Simultaneously, black hole growth is tightly linked to the dynamical state of the host galaxy. In low-mass, turbulent systems, stellar feedback can suppress nuclear gas inflows, delaying black hole growth. Only when galaxies become sufficiently massive and dynamically settled can gas efficiently reach galactic centers to fuel sustained accretion. These processes also have important implications for the spin evolution of black holes or how fast they coalesce, which can reflect the varying modes of accretion and feedback across cosmic time.
- Speaker: Yohan Dubois (Institut d’Astrophysique de Paris)
- Thursday 05 June 2025, 16:00-17:00
- Venue: Hoyle Lecture Theatre, Institute of Astronomy.
- Series: Institute of Astronomy Colloquia; organiser: Matthew Grayling.
Fri 06 Jun 11:30: Exploring the End of Reionization
Abstract not available
- Speaker: George Becker (UC Riverside)
- Friday 06 June 2025, 11:30-12:30
- Venue: Ryle Seminar Room, KICC + online.
- Series: Galaxies Discussion Group; organiser: Sandro Tacchella.
Wed 11 Jun 13:15: Neurodiversity and Communication Styles
Dr Maria Dias, Neurodiversity Adviser at the Accessibility and Disability Resource Centre (ADRC) and St Catharine’s College, will explore how people with different neurotypes communicate in unique ways, and why understanding these differences is important for creating more inclusive and supportive environments. Whether you’re neurodivergent yourself, work with neurodivergent people, or just want to learn more, this talk is for you. There will be time for questions and open discussion at the end.
- Speaker: Maria Dias, Neurodiversity Adviser at the Accessibility and Disability Resource Centre (ADRC) and St Catharine’s College
- Wednesday 11 June 2025, 13:15-14:05
- Venue: The Hoyle Lecture Theatre + Zoom .
- Series: Institute of Astronomy Seminars; organiser: Cristiano Longarini.
Wed 11 Jun 13:15: Neurodiversity and Communication Styles
Dr Maria Dias, Neurodiversity Adviser at the Accessibility and Disability Resource Centre (ADRC) and St Catharine’s College, will explore how people with different neurotypes communicate in unique ways, and why understanding these differences is important for creating more inclusive and supportive environments. Whether you’re neurodivergent yourself, work with neurodivergent people, or just want to learn more, this talk is for you. There will be time for questions and open discussion at the end.
- Speaker: Maria Dias, Neurodiversity Adviser at the Accessibility and Disability Resource Centre (ADRC) and St Catharine’s College
- Wednesday 11 June 2025, 13:15-14:05
- Venue: The Hoyle Lecture Theatre + Zoom .
- Series: Institute of Astronomy Seminars; organiser: Cristiano Longarini.
Mon 02 Jun 16:00: Imaging and Design with Differentiable Physics Models
The technology that underpins machine learning – differentiable programming – is poised to revolutionise astronomy, making it possible for the first time to fit very high dimensional models: hierarchical models describing many objects; the sensitivity of millions of pixels in a detector; models of images or spectra with very many free parameters; or neural networks that represent physics we cannot easily solve in closed form. It also enables fundamental information-theoretic quantities like the Fisher information to be calculated, allowing for determination and optimization of the information content of an experiment. I will discuss how we apply this to the James Webb interferometer experiment, to provide a data-driven self-calibration of the telescope’s highest resolution mode and its difficult systematics; to design the Toliman Space Telescope to do high-precision, distortion-tolerant astrometry; and give an overview of related work on interferometry, transits and AGN reverberation mapping in our group.
- Speaker: Benjamin Pope (Macquarie University)
- Monday 02 June 2025, 16:00-17:00
- Venue: Martin Ryle Seminar Room, KICC.
- Series: Astro Data Science Discussion Group; organiser: km723.
Gas meets Kozai: the influence of a gas-rich accretion disc on hierarchical triples undergoing von Zeipel-Lidov-Kozai oscillations
Gas meets Kozai: the influence of a gas-rich accretion disc on hierarchical triples undergoing von Zeipel-Lidov-Kozai oscillations
Mon 09 Jun 13:00: Pulsar Timing Arrays and Astrometry: Going Beyond the Hellings-Downs correlation
The detection of gravitational waves (GWs) by pulsar timing arrays (PTAs) opens new avenues for probing the physics of GW sources at nanohertz frequencies. In the same frequency band, astrometric observations may also enable future GW detections. It is therefore important to investigate the potential for cross-correlating these two complementary approaches. Accordingly, I will discuss three topics related to the characterization of the stochastic gravitational-wave background using pulsar timing arrays and astrometry. The potential detection of its kinematic dipole. The prospects for measuring its circular polarization. A new method for identifying the possible presence of scalar polarization in the GW background.
- Speaker: Gianmassimo Tasinato (Swansea University)
- Monday 09 June 2025, 13:00-14:00
- Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
- Series: Cosmology Lunch; organiser: Thomas Colas.
Mon 02 Jun 13:00: Cracks in the Standard Cosmological Model: Anomalies, Tensions, and Hints of New Physics
The ΛCDM model has long served as the standard paradigm in cosmology, offering a remarkably successful description of the Universe’s evolution. Yet, as observational precision continues to improve, persistent tensions have emerged across a range of probes, including the well-known Hubble constant discrepancy. While individual datasets may each align with ΛCDM, their collective interpretation reveals significant discordances that challenge the model’s internal consistency. In this talk, I will review the most prominent tensions in modern cosmology and assess their implications. I will present recent results pointing to hints of dynamical dark energy and interactions within the dark sector. I will also reflect on the growing influence of methodological choices, such as dataset selection and model assumptions, in shaping our cosmological conclusions.
- Speaker: Eleonora Di Valentino (University of Sheffield)
- Monday 02 June 2025, 13:00-14:00
- Venue: SPECIAL LOCATION - CMS, MR4, Pav A basement.
- Series: Cosmology Lunch; organiser: Thomas Colas.
Hubble Spies Paired Pinwheel on Its Own
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2 min read
Hubble Spies Paired Pinwheel on Its Own This NASA Hubble Space Telescope image features the beautiful barred spiral galaxy NGC 3507 ESA/Hubble & NASA, D. Thilker
A single member of a galaxy pair takes centerstage in this NASA/ESA Hubble Space Telescope image. This beautiful spiral galaxy is NGC 3507, which is situated about 46 million light-years away in the constellation Leo (the Lion). NGC 3507’s classification is a barred spiral because the galaxy’s sweeping spiral arms emerge from the ends of a central bar of stars rather than the central core of the galaxy.
Though pictured solo here, NGC 3507 actually travels the universe with a galactic partner named NGC 3501 that is located outside the frame. While NGC 3507 is a quintessential galactic pinwheel, its partner resembles a streak of quicksilver across the sky. Despite looking completely different, both are spiral galaxies, simply seen from different angles.
For galaxies that are just a few tens of millions of light-years away, like NGC 3507 and NGC 3501, features like spiral arms, dusty gas clouds, and brilliant star clusters are on full display. More distant galaxies appear less detailed. See if you can spot any faraway galaxies in this image: they tend to be orange or yellow and can be anywhere from circular and starlike to narrow and elongated, with hints of spiral arms. Astronomers use instruments called spectrometers to split the light from these distant galaxies to study the nature of these objects in the early universe.
In addition to these far-flung companions, a much nearer object joins NGC 3507. The object is marked by four spikes of light: a star within the Milky Way, a mere 436 light-years away from Earth.
Text Credit: ESA/Hubble
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Claire Andreoli (claire.andreoli@nasa.gov)
NASA’s Goddard Space Flight Center, Greenbelt, MD
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Science Behind the Discoveries
Tue 10 Jun 16:00: Title to be confirmed
Abstract not available
- Speaker: Daniel Muthukrishna (MIT)
- Tuesday 10 June 2025, 16:00-17:00
- Venue: Martin Ryle Seminar Room, KICC.
- Series: Astro Data Science Discussion Group; organiser: km723.
Wed 04 Jun 13:40: GPU Accelerated Sampling and Model Comparison
This talk introduces a natively vectorized implementation of the Nested Sampling algorithm, enabling deployment of the entire inference process onto GPUs for massive acceleration. I will start by reviewing the benefits, and necessity, of the paradigm shift towards vectorized compute in the physical sciences. After a brief review of the how (and why) of Bayesian inference in Astronomy and Cosmology, I will then explore the nuances and challenges of taking some of the widely used inference algorithms within this community, in particular nested sampling, to the GPU accelerated frontier. Lastly I’ll present some practical benefit that this speedup can bring and comment on how this technical development can help push the boundaries of what we can achieve in the physical sciences.
- Speaker: David Yallup / IoA
- Wednesday 04 June 2025, 13:40-14:05
- Venue: The Hoyle Lecture Theatre + Zoom .
- Series: Institute of Astronomy Seminars; organiser: .
Wed 04 Jun 13:40: GPU Accelerated Sampling and Model Comparison
This talk introduces a natively vectorized implementation of the Nested Sampling algorithm, enabling deployment of the entire inference process onto GPUs for massive acceleration. I will start by reviewing the benefits, and necessity, of the paradigm shift towards vectorized compute in the physical sciences. After a brief review of the how (and why) of Bayesian inference in Astronomy and Cosmology, I will then explore the nuances and challenges of taking some of the widely used inference algorithms within this community, in particular nested sampling, to the GPU accelerated frontier. Lastly I’ll present some practical benefit that this speedup can bring and comment on how this technical development can help push the boundaries of what we can achieve in the physical sciences.
- Speaker: David Yallup / IoA
- Wednesday 04 June 2025, 13:40-14:05
- Venue: The Hoyle Lecture Theatre + Zoom .
- Series: Institute of Astronomy Seminars; organiser: .
Tue 21 Oct 11:15: Title TBC
Abstract TBC
- Speaker: Dr. Weiyang Wang (University of Chinese Academy of Sciences)
- Tuesday 21 October 2025, 11:15-12:00
- Venue: TBC.
- Series: Hills Coffee Talks; organiser: Charles Walker.