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Uniqueness of extremal black holes in de Sitter

Uniqueness theorems for black holes with a cosmological constant are only known in a few limited cases. In my talk I present a recent uniqueness theorem for the extremal Schwarzschild-de Sitter black hole within the class of analytic vacuum spacetimes with a positive cosmological constant containing a static extremal Killing horizon. The proof is based on establishing the uniqueness of transverse deformations to the near-horizon geometry at each order in the transverse parameter. I also present a generalisation to charged extremal black holes in de Sitter and discuss the analogous problem in the case of negative cosmological constant. The talk is based on 2309.04238 [gr-qc] and 2403.08467 [gr-qc].

• Speaker: Dávid Katona, The University of Edinburgh
• Friday 26 April 2024, 13:00-14:00
• Venue: Potter room/Zoom.
• Series: DAMTP Friday GR Seminar; organiser: Xi Tong.

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Neural ratio estimation: the future of supernova cosmology?

Simulation-based inference (SBI) has the potential to revolutionise how we do supernova cosmology and let us incorporate arbitrarily complex effects within a Bayesian model. I will present recent work which sought to validate neural ratio estimation (NRE) by comparing NRE -derived posteriors on supernova properties to those obtained with a likelihood-based MCMC approach for the same data, and then discuss how NRE and SBI in general provide a pathway towards a model extending all the way from type Ia supernova light curves to cosmological parameters as part of a single analysis.

• Speaker: Matthew Grayling (University of Cambridge)
• Wednesday 24 April 2024, 10:00-11:00
• Venue: Martin Ryle Seminar Room, KICC.
• Series: Astro Data Science Discussion Group; organiser: David Yallup.

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arXiv:2404.10486v2 Announce Type: replace Abstract: Gravitational waves from black-hole merging events have revealed a population of extra-galactic BHs residing in short-period binaries with masses that are higher than expected based on most stellar evolution models - and also higher than known stellar-origin black holes in our Galaxy. It has been proposed that those high-mass BHs are the remnants of massive metal-poor stars. Gaia astrometry is expected to uncover many Galactic wide-binary systems containing dormant BHs, which may not have been detected before. The study of this population will provide new information on the BH-mass distribution in binaries and shed light on their formation mechanisms and progenitors. As part of the validation efforts in preparation for the fourth Gaia data release (DR4), we analysed the preliminary astrometric binary solutions, obtained by the Gaia Non-Single Star pipeline, to verify their significance and to minimise false-detection rates in high-mass-function orbital solutions. The astrometric binary solution of one source, Gaia BH3, implies the presence of a 32.70 \pm 0.82 M\odot BH in a binary system with a period of 11.6 yr. Gaia radial velocities independently validate the astrometric orbit. Broad-band photometric and spectroscopic data show that the visible component is an old, very metal-poor giant of the Galactic halo, at a distance of 590 pc. The BH in the Gaia BH3 system is more massive than any other Galactic stellar-origin BH known thus far. The low metallicity of the star companion supports the scenario that metal-poor massive stars are progenitors of the high-mass BHs detected by gravitational-wave telescopes. The Galactic orbit of the system and its metallicity indicate that it might belong to the Sequoia halo substructure. Alternatively, and more plausibly, it could belong to the ED-2 stream, which likely originated from a globular cluster that had been disrupted by the Milky Way.

arXiv:2404.12585v1 Announce Type: new Abstract: The attenuation of Ly$\alpha$ photons by neutral hydrogen in the intergalactic medium (IGM) at $z\gtrsim5$ continues to be a powerful probe for studying the epoch of reionisation. Given a framework to estimate the intrinsic (true) Ly$\alpha$ emission of high-$z$ sources, one can infer the ionisation state of the IGM during reionisation. In this work, we use the enlarged XQR-30 sample of 42 high-resolution and high-SNR QSO spectra between $5.8\lesssim\,z\lesssim\,6.6$ obtained with VLT/X-Shooter to place constraints on the IGM neutral fraction. This is achieved using our existing Bayesian QSO reconstruction framework which accounts for uncertainties such as the: (i) posterior distribution of predicted intrinsic Ly$\alpha$ emission profiles (obtained via covariance matrix reconstruction of the Ly$\alpha$ and N V emission lines from unattenuated high-ionisation emission line profiles; C IV, Si IV + O IV] and C III]) and (ii) distribution of ionised regions within the IGM using synthetic damping wing profiles drawn from a $1.6^3$ Gpc$^3$ reionisation simulation. Following careful quality control, we used 23 of the 42 available QSOs to obtain constraints/limits on the IGM neutral fraction during the tail-end of reionisation. Our median and 68th percentile constraints on the IGM neutral fraction are: $0.20\substack{+0.14\\-0.12}$ and $0.29\substack{+0.14\\-0.13}$ at $z = 6.15$~and 6.35. Further, we also report 68th percentile upper-limits of $\bar{x}_{\mathrm{H\,{\scriptscriptstyle I}}}

The US space agency is seeking a cheaper, faster solution to bring Martian rocks to Earth for study.

An Australian bull ant is the first animal known to use the patterns produced by polarised moonlight to navigate its environment

Which universes does the no-boundary wave function favour?

Please notice the unusual schedule (9:45am) and location (MR9) due to previous overlaps with the Dirac lunch and Dirac lecture.

• Speaker: Jean-Luc Lehners (MPI for Gravitational Physics, Potsdam)
• Monday 13 May 2024, 10:00-11:00
• Venue: CMS, Pav. B, MR9 (B0.09) .
• Series: Cosmology Lunch; organiser: Thomas Colas.

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Nature, Published online: 19 April 2024; doi:10.1038/d41586-024-01073-w

Antarctic observatory gathers the first clear evidence of mysterious subatomic particles from space.

It can be difficult to figure out how to move a spacecraft from one orbit to another, but a trick from knot theory can help find spots where shifting orbits becomes easy

Stellar activity mitigation in radial velocity measurements

Over the past decades, the radial velocity (RV) community has made tremendous leaps forward in detecting and characterising ever smaller and lighter exoplanets. This trend has been interrupted in recent years, as planetary RV signals below 1 m/s are drowned out by the stars’ activity. The detection of Earth analogues producing an RV effect of about 10 cm/s is therefore currently out of reach. Several avenues are being explored to restore the trend towards the detection of increasingly less massive planets. These include improvements in (1) instruments, (2) observing strategies, (3) RV extraction techniques, (4) stellar activity monitoring, and (5) stellar activity modelling. In this talk, I will focus on points (4), and (5). I will provide an overview of stellar activity mitigation techniques and show how a proxy for stellar magnetic activity induced RV variations can be extracted from intensity spectra in the visible wavelength range, providing an independent estimate of the evolution of the magnetic field.

• Speaker: Florian Lienhard (ETH Zurich)
• Tuesday 30 April 2024, 13:00-14:00
• Venue: Battcock coffee area + ONLINE - Details to be sent by email.
• Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.

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The recently discovered black holes in wide binaries by Gaia astrometry

I will discuss the recent discovery of the three black holes (BH) by Gaia astrometry, concentrating on BH3 , with a mass of 33 M_solar, which is orbited by a very metal poor giant in an orbit of 12 years. The BH in the Gaia BH3 system is more massive than any other Galactic stellar-origin BH known. The Galactic orbit of the system and its metallicity indicate that it probably belongs to the ED-2 stream, which likely originated from a globular cluster that was disrupted by the Milky Way.

• Speaker: Tsevi Mazeh (Tel Aviv)
• Tuesday 07 May 2024, 11:30-12:30
• Venue: Hoyle Lecture Theatre + ONLINE - Details will be sent by email.
• Series: Kavli Institute for Cosmology Seminars; organiser: Alison Wilson.

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arXiv:2404.12157v1 Announce Type: new Abstract: Future data provided by the \Euclid mission will allow us to better understand the cosmic history of the Universe. A metric of its performance is the figure-of-merit (FoM) of dark energy, usually estimated with Fisher forecasts. The expected FoM has previously been estimated taking into account the two main probes of \Euclid, namely the three-dimensional clustering of the spectroscopic galaxy sample, and the so-called 3$\times$2\,pt signal from the photometric sample (i.e., the weak lensing signal, the galaxy clustering, and their cross-correlation). So far, these two probes have been treated as independent. In this paper, we introduce a new observable given by the ratio of the (angular) two-point correlation function of galaxies from the two surveys. For identical (normalised) selection functions, this observable is unaffected by sampling noise, and its variance is solely controlled by Poisson noise. We present forecasts for \Euclid where this multi-tracer method is applied and is particularly relevant because the two surveys will cover the same area of the sky. This method allows for the exploitation of the combination of the spectroscopic and photometric samples. When the correlation between this new observable and the other probes is not taken into account, a significant gain is obtained in the FoM, as well as in the constraints on other cosmological parameters. The benefit is more pronounced for a commonly investigated modified gravity model, namely the $\gamma$ parametrisation of the growth factor. However, the correlation between the different probes is found to be significant and hence the actual gain is uncertain. We present various strategies for circumventing this issue and still extract useful information from the new observable.

Science, Volume 384, Issue 6693, Page 348-352, April 2024.

Science, Volume 384, Issue 6693, Page 255-256, April 2024.

Science, Volume 384, Issue 6693, Page 258-259, April 2024.

This animation is an artist’s concept of Loki Patera, a lava lake on Jupiter’s moon Io, made using data from the JunoCam imager aboard NASA’s Juno spacecraft. With multiple islands in its interior, Loki is a depression filled with magma and rimmed with molten lava. Credit: NASA/JPL-Caltech/SwRI/MSSS

Imagery from the solar-powered spacecraft provides close-ups of intriguing features on the hellish Jovian moon.

Scientists on NASA’s Juno mission to Jupiter have transformed data collected during two recent flybys of Io into animations that highlight two of the Jovian moon’s most dramatic features: a mountain and an almost glass-smooth lake of cooling lava. Other recent science results from the solar-powered spacecraft include updates on Jupiter’s polar cyclones and water abundance.

The new findings were announced Wednesday, April 16, by Juno’s principal investigator Scott Bolton during a news conference at the European Geophysical Union General Assembly in Vienna.

Juno made extremely close flybys of Io in December 2023 and February 2024, getting within about 930 miles (1,500 kilometers) of the surface, obtaining the first close-up images of the moon’s northern latitudes.

“Io is simply littered with volcanoes, and we caught a few of them in action,” said Bolton. “We also got some great close-ups and other data on a 200-kilometer-long (127-mile-long) lava lake called Loki Patera. There is amazing detail showing these crazy islands embedded in the middle of a potentially magma lake rimmed with hot lava. The specular reflection our instruments recorded of the lake suggests parts of Io’s surface are as smooth as glass, reminiscent of volcanically created obsidian glass on Earth.”

The JunoCam instrument on NASA’s Juno captured this view of Jupiter’s moon Io — with the first-ever image of its south polar region — during the spacecraft’s 60th flyby of Jupiter on April 9.Image credit: NASA/JPL-Caltech/SwRI/MSSS. Image processing: Gerald Eichstädt/Thomas Thomopoulos (CC BY).

Maps generated with data collected by Juno’s Microwave Radiometer (MWR) instrument reveal Io not only has a surface that is relatively smooth compared to Jupiter’s other Galilean moons, but also has poles that are colder than middle latitudes.

Pole Position

During Juno’s extended mission, the spacecraft flies closer to the north pole of Jupiter with each pass. This changing orientation allows the MWR instrument to improve its resolution of Jupiter’s northern polar cyclones. The data allows multiwavelength comparisons of the poles, revealing that not all polar cyclones are created equal.

“Perhaps most striking example of this disparity can be found with the central cyclone at Jupiter’s north pole,” said Steve Levin, Juno’s project scientist at NASA’s Jet Propulsion Laboratory in Southern California. “It is clearly visible in both infrared and visible light images, but its microwave signature is nowhere near as strong as other nearby storms. This tells us that its subsurface structure must be very different from these other cyclones. The MWR team continues to collect more and better microwave data with every orbit, so we anticipate developing a more detailed 3D map of these intriguing polar storms.”

Jovian Water

One of the mission’s primary science goals is to collect data that could help scientists better understand Jupiter’s water abundance. To do this, the Juno science team isn’t hunting for liquid water. Instead, they are looking to quantify the presence of oxygen and hydrogen molecules (the molecules that make up water) in Jupiter’s atmosphere. An accurate estimate is critical to piecing together the puzzle of our solar system’s formation.

Created using data collected by the JunoCam imager aboard NASA’s Juno during flybys in December 2023 and February 2024, this animation is an artist’s concept of a feature on the Jovian moon Io that the mission science team nicknamed “Steeple Mountain.” Credit: NASA/JPL-Caltech/SwRI/MSSS

Jupiter was likely the first planet to form, and it contains most of the gas and dust that wasn’t incorporated into the Sun. Water abundance also has important implications for the gas giant’s meteorology (including how wind currents flow on Jupiter) and internal structure.

In 1995, NASA’s Galileo probe provided an early dataset on Jupiter’s water abundance during the spacecraft’s 57-minute descent into the Jovian atmosphere. But the data created more questions than answers, indicating the gas giant’s atmosphere was unexpectedly hot and — contrary to what computer models had indicated — bereft of water.

“The probe did amazing science, but its data was so far afield from our models of Jupiter’s water abundance that we considered whether the location it sampled could be an outlier. But before Juno, we couldn’t confirm,” said Bolton. “Now, with recent results made with MWR data, we have nailed down that the water abundance near Jupiter’s equator is roughly three to four times the solar abundance when compared to hydrogen. This definitively demonstrates that the Galileo probe’s entry site was an anomalously dry, desert-like region.”

The results support the belief that the during formation of our solar system, water-ice material may have been the source of the heavy element enrichment (chemical elements heavier than hydrogen and helium that were accreted by Jupiter) during the gas giant’s formation and/or evolution. The formation of Jupiter remains puzzling, because Juno results on the core of the gas giant suggest a very low water abundance — a mystery that scientists are still trying to sort out. 

Data during the remainder of Juno’s extended mission may help, both by enabling scientists to compare Jupiter’s water abundance near the polar regions to the equatorial region and by shedding additional light on the structure of the planet’s dilute core. 

During Juno’s most recent flyby of Io, on April 9, the spacecraft came within about 10,250 miles (16,500 kilometers) of the moon’s surface. It will execute its 61st flyby of Jupiter on May 12.

More About the Mission

NASA’s Jet Propulsion Laboratory, a division of Caltech in Pasadena, California, manages the Juno mission for the principal investigator, Scott Bolton, of the Southwest Research Institute in San Antonio. Juno is part of NASA’s New Frontiers Program, which is managed at NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate in Washington. The Italian Space Agency (ASI) funded the Jovian InfraRed Auroral Mapper. Lockheed Martin Space in Denver built and operates the spacecraft.

More information about Juno is available at:

https://www.nasa.gov/juno

News Media Contacts

DC Agle
Jet Propulsion Laboratory, Pasadena, Calif.
818-393-9011
agle@jpl.nasa.gov

Karen Fox / Charles Blue
NASA Headquarters, Washington
301-286-6284 / 202-802-5345
karen.c.fox@nasa.gov / charles.e.blue@nasa.gov

Deb Schmid
Southwest Research Institute, San Antonio
210-522-2254
dschmid@swri.org

2024-045

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Details Last Updated Apr 18, 2024 Related Terms

• Juno
• Io
• Jet Propulsion Laboratory
• Jupiter
• Jupiter Moons
• The Solar System

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Nature, Published online: 18 April 2024; doi:10.1038/d41586-024-01138-w

Understanding the volcanic moon’s history could offer fresh insights into conditions on early Earth.

Measurements of sulphur isotopes in Io’s atmosphere show that the moon may have been volcanically active for its entire lifetime

Dynamical Gravastars

I give new results for ``gravastars’’, which are horizonless compact objects that closely mimic mathematical black holes in their exterior geometry, but for which $g_{00}$ is always positive. In my initial formulation, they result from solving the Tolman-Oppenheimer-Volkoff (TOV) equations for relativistic stellar structure, which require continuous pressure, but with an interior density jump from a normal matter equation of state, to an equation of state where pressure plus density approximately sum to zero. We present Mathematica notebooks solving the TOV equations, in which the structure of the gravastar is entirely governed by the Einstein-Hilbert gravitational action (with zero cosmological constant) together with the matter equation of state, with radii where structural changes occur emerging from the dynamics, rather than being specified in advance as in the original Mazur-Mottola gravastars.

My more recent work with a student shows that the interesting ``simulated horizon’’ structure of dynamical gravastars is a property solely of the exterior TOV equations for relativistic matter with appropriate small radius boundary conditions, and will be present for a large class of interior equations of state. The exterior TOV equations can be rewritten in rescaling-invariant form, leading to a two dimensional autonomous system of differential equations which are now being studied numerically and analytically , and for which hopefully some rigorous results can be proved.

• Speaker: Stephen Adler, Princeton, Institute for Advanced Study
• Friday 19 April 2024, 13:00-14:00
• Venue: Potter room/Zoom: https://cam-ac-uk.zoom.us/j/85670039340?pwd=MmRxMDdYMGY5b0IzSm9QRUJmWFNVUT09.
• Series: DAMTP Friday GR Seminar; organiser: Xi Tong.

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arXiv:2312.03847v2 Announce Type: replace Abstract: The oldest stars in the Milky Way (born in the first few billion years) are expected to have a high density in the inner few kpc, spatially overlapping with the Galactic bulge. We use spectroscopic data from the Pristine Inner Galaxy Survey (PIGS) to study the dynamical properties of ancient, metal-poor inner Galaxy stars. We compute distances using StarHorse, and orbital properties in a barred Galactic potential. With this paper, we release the spectroscopic AAT/PIGS catalogue (13 235 stars). We find that most PIGS stars have orbits typical for a pressure-supported population. The fraction of stars confined to the inner Galaxy decreases with decreasing metallicity, but many very metal-poor stars (VMP, [Fe/H]