Shining a Light on Dark Matter. In December's episode, we have delved into the archive for an interview with Grace Lawrence from 2022; she talks with Jonathan and Imogen about her work in dark matter detection. Nastassia and Louisa answer some listeners’ questions in Ask an Astronomer, delving into wormhole exit points and pringle-shaped universes.

The News

Unveiling Cygnus X-3: XRISM Explores a Hidden Black Hole and Stellar Winds

Astronomers using the Japanese-led XRISM telescope, operated jointly by JAXA and NASA, have unveiled incredible details about Cygnus X-3, a fascinating binary system located 32,000 light-years away in the constellation Cygnus, the Swan.

Cygnus X-3 is thought to host a 'hidden' black hole paired with a massive Wolf-Rayet star, a rare type of star that produces powerful stellar winds. These two celestial bodies are so close that they orbit each other in just under 5 hours! The intense interaction between the black hole and the massive star creates high-energy X-rays, making it an ideal target for XRISM, which excels in detecting X-ray emissions.

During an 18-hour observation earlier this year, XRISM’s Resolve instrument captured a high-resolution spectrum of the gases flowing within this system. It revealed how the strong stellar winds from the Wolf-Rayet star are swept up and heated by the suspected black hole, creating turbulent gas that moves at astonishing speeds — up to 930,000 miles per hour, or 1,000 times the speed of sound!

What’s fascinating is that Cygnus X-3 is shrouded in dust and gas, making it invisible in visible light. But X-rays and radio waves can pierce through, allowing astronomers to study the system. XRISM’s data shows that much of this gas is moving toward us — a phenomenon captured as 'blueshifting' in the spectrum. By analyzing ionized iron in the spectrum, scientists hope to confirm whether the compact object in Cygnus X-3 is truly a black hole.

This groundbreaking observation not only highlights the power of XRISM but also offers a deeper glimpse into how stars and black holes interact in extreme environments.

Never seen before Jupiter Mass Binaries in the Orion Nebula now have an explanation!

Last year, Pearson and McCaughrean (2023) identified 42 pairs of binary brown dwarfs with each star having roughly the same mass as jupyter in the Trapezium cluster in the Orion nebula using the James Webb Space Telescope. Isolated jupyter mass objects are relatively rare so seeing them in pairs was completely unexpected. These JuMBOs as they are called are part of a flurry of other free floating planets or FFPs in the nebula. They composed 9% of all the FFPs detected which is an incredibly high fraction when compared to objects of a mass that is a little higher than these.

The components of the JuMBOs have mass ranging between 0.7 to 13 jupiter masses with separations in the range of 10s to 100s of AUs. There are many models to explain how brown dwarfs can form but so far most do not have conditions for which they would form in binary systems. Whitworth and Zinnecker (2004) put forward a model where photoionisation from nearby type A stars photoionise cores in which protostars are forming. Type A stars are high mass blue stars that have a strong hydrogen line emission. These emissions drive an ionisation shock front into the prestellar core, compressing the inner layers whilst simultaneously evaporating the outer layers. This results in the very efficient formation of sub-solar mass objects.

Diamond and Parker (2024) looked at the location of those JuMBOs within the cloud and found that they all appear within a radius of ∼0.6 pc of the stars, which is the size of the bubbles created by the type A stars in the Orion system. And the most amazing thing is that they apply the Whitworth and Zinnecker to models of binary systems and find what type of star would have resulted from the original binary had they not been photo-eroded and they found that these stars would be type A stars themselves !

Interview with Dr Grace Lawrence

In this interview, Grace Lawrence talks about all things dark matter. Her work focuses on the direct detection of dark matter, using simulations of Milky Way type galaxies to predict possible dark matter signals. Due to the relative motion of the sun moving through the galaxy and the earth moving around the sun, we expect dark matter signals to change with the season as the earth's relative velocity to the galaxy changes. Grace discusses this key feature that dark matter detectors use to distinguish true detections from a general particle background. Grace is also working with the Sabre collaboration, working to reproduce DAMA/LIBRA's controversial dark matter detection.

Ask an Astronomer

Hi Listeners! This month, we have taken on a selection of questions from listeners that we have accrued over the year - Today is the day you get a reply from us! We have asked around the department to find some answers. We will be leaving questions on our kitchen whiteboard for JBCA academics and students to answer, with the best answer achieving a Freddo (other chocolate bars are available!). Your questions have certainly made for interesting lunch time conversations!

Q: TK Arsipe asks about white holes, and their potential place within our universe.
A: For those who haven’t heard, a white hole is the theoretical counterpart to a black hole; matter falls into a black hole and cannot escape, whereas a white hole would see matter flowing out and unable to enter. They would be extremely luminous objects in our universe, but with no real ideas on how they would form and their place within our existing theories of the universe. White holes are the exit point for theoretical wormholes, but the sci-fi dream of interstellar ‘portals’ continues to face healthy scepticism in science - black holes are predicted to be singularities, with so little understanding about their nature. The momentous computational power required by the Event Horizon Telescope to image M87 and Sgr A* must indicate how tricky for astronomers to understand black holes, never mind their theoretical counterparts.

So when we asked the department for their thoughts, there were mixed emotions about answering this question on air. Arguably, astronomy is all about observing the universe, and with no real evidence or detections made of white holes, this question would be a theoretician’s dream! Just not an astronomer’s…

Q: What is the shape of the universe?
A: General relativity predicts that the universe can take one of three possible shapes : open, flat or closed . These geometries aren’t just abstract ideas—they shape how we understand the universe’s past, present, and ultimately, it’s fate. Mathematically, cosmologists describe the geometry of the universe using a dimensionless density parameter denoted Omega. This parameter compares the universe’s total energy density to a critical value known as the critical density, which is the threshold density required for the universe to expand forever at a decreasing rate. Today, in our dark energy dominated era, the critical density is estimated at 9.5 kg per m3. Einsteins equations tell us that the geometry of the universe is influenced by its matter content, A universe containing matter cannot be static. It must be either expanding or contracting. So its geometry will in turn, decide, as we will see, on the fate of the universe.In other words, the value of this density parameter omega determines the universe's geometry and influences how it evolves over time. Let’s go through the 3 possible topologies :

Ω=1: The universe is flat, with a density precisely equal to the critical density. Such a universe will expand forever, though the rate of expansion will slow down over time. In this geometry, space is infinite, parallel lines remain parallel, and the angles of a triangle sum to exactly 180°. So yeah Imagine an infinite, never-ending plane.
Ω>1: Now we’re talking about a closed universe, with a density exceeding the critical value. Here, gravitational attraction is strong enough to eventually halt the expansion, and the universe collapses in on itself in a “big crunch.” This universe is finite but without boundaries, much like the surface of a sphere, where parallel lines converge, and triangle angles add up to more than 180°.
Ω<1: The universe is open, with a density below the critical value. In this case, the universe expands forever at an accelerating rate.Picture a saddle or a Pringle. In this geometry, space is infinite, parallel lines diverge, and the angles of a triangle sum to less than 180°.

At that point you should be wondering, so what is the actual density of the universe ? Of course our answer is going to be slightly underwhelming here, since determining the actual density of the universe requires measurements of the matter and energy content in all its forms, including ordinary matter, dark matter, and dark energy. Current measurements of fluctuations in the cosmic microwave background suggest that the universe is flat. To our present knowledge, all major observations, including those from missions like WMAP, the Atacama Cosmology Telescope, and Planck, reveals that the universe's total density is very close to the critical density, with Ω =1.02, suggesting that the universe if very close to flat, consistent what is known as the Lambda Cold Dark Matter model. According to this model, matter makes up approximately 27% of the total density, with only 4% being ordinary (baryonic) matter- the kind that forms stars, planets, and galaxies. The remaining 23% is dark matter, the mysterious component detectable only through its gravitational influence. Meanwhile, dark energy, accounting for 73% of the total density, is the dominant driver of the universe's accelerated expansion.

It is worth noting that some researchers, analysing gravitational lensing in the CMB(how much the light from the CMB has been deflected by the gravity of matter in its path) have proposed that the universe might have slight positive curvature, suggesting a closed universe. However, most evidence supports flatness, and any deviations are often attributed to statistical anomalies or limitations in data. Finally, when we say the universe is flat, what we truly mean is that the observable universe—the portion we can see, spanning 93 billion light-years across—is consistent with being part of a larger, three-dimensional flat surface. Beyond that horizon, the true shape of the universe remains a mystery.

Q: Does the universe have an edge?
A: The universe does not have a physical edge—there is no wall, border, or boundary marking the end of space. However, the observable universe does have an apparent limit, known as the cosmological horizon, which is determined by the farthest distance light has traveled to reach us since the Big Bang. Beyond this horizon, the universe likely continues, but it is unobservable because light from those regions has not had enough time to reach us. A close, finite, sphere like universe would still have no edges since the geometry naturally loops back on itself. For now, though, the evidence points to a flat universe—a boundless expanse that could continue to stretch infinitely, shaped by the balance of its energy and matter.

Q: Would we ever be able to obtain any data from the areas of the universe which lie beyond our cosmological horizon? Scientists are wonderfully good at teasing out data from the most unlikely sources. It appears that we are limited to observing whatever photons, neutrinos, and gravitational waves have had time to cross the universe to reach us, but is there a workaround according to our current understanding of physics?
A: Even though the universe may not have an edge, our understanding can only extend as far as light can travel. Messages across the universe are limited by the speed of light, Astronomy still heavily relies on electromagnetic waves; neutrinos and gravitational waves remain under-explored for observing our universe. But ultimately, we are bound by the speed of light, which sets the limit for the observable universe.

Interview : Dr Grace Lawrence and Imogen Towler and Jonathan Wong
Presenters : Jessy Marin and Bijas Najimudeen
Editors : Jordan Norris, Jamie Incley and Tobias Russell
Website : Lilia Correa Magnus & George Bendo & Phoebe Ryder
Producer : Lily Correa Magnus and Phoebe Ryder
Cover Art : The ring of dark matter illustrated in blue around ZwCl0024+1652.
CREDIT:ESA/Hubble (M. Kornmesser and L. L. Christensen).