Moon might have formed in five hours

They say Rome wasn’t built in a day, but the Moon might have taken just five hours to form from the debris of a collision between Earth and a Mars-sized space rock. Simulations have tended to focus on the size of proto-Earth and ‘Theia’, the body that evidence suggests once struck our home planet. If Earth and Theia were both hot and smooshy, the chunks that eventually formed the Moon would have stayed largely intact — making it form more quickly — than if the two smashees were cool.

How an ancient collision with another galaxy transformed the Milky Way

Astrophysicists have found evidence that the Milky Way collided and merged with a dwarf galaxy around 12 billion years ago. Using the Hubble Space Telescope, the team found that the makeup of some globular clusters — groups of stars held tightly together by gravity — doesn’t match that of those that are thought to be native to the Milky Way or that arrived during a later merger with another dwarf galaxy known as the Gaia–Sausage–Enceladus. “We do not know how our house was built,” says astrophysicist and study co-author Davide Massari. But these findings point to “where the first significant batch of bricks came from”.

Are dark matter and dark energy one thing?

The Universe is a dark place: around 70% of it seems to be dark energy, a mysterious force that seems to drive accelerating expansion; and dark matter, an invisible ‘something’ that holds galaxies together. These two enigmas were thought to have little in common except their names. Now some theorists are asking if they might be linked though a ‘dark dimension’ — one of the six or seven ‘extra’ dimensions posited by string theory. This idea could account for evidence from the Dark Energy Spectroscopic Instrument (DESI) that the strength of dark energy has gone up and down over time.

Blogger Comments:

A note of caution: This article presents a chain of theoretical speculation that extends from possible time-variation in dark energy, to interactions between dark matter and dark energy, to the introduction of extra dimensions within string-theoretic frameworks. While each step in this sequence is formally motivated within its respective modelling context, none constitutes empirical confirmation of the entities it introduces. The overall narrative can therefore create a misleading impression of convergence toward an established physical picture, when in fact it remains a stack of contingent hypotheses layered on top of one another.

More generally, the discussion illustrates a recurring feature of popular theoretical physics: the gradual replacement of observational uncertainty with ontological confidence, as models are re-described as descriptions of “things” rather than as constrained formal responses to data. It is important to keep distinct what is observed, what is modelled, and what is inferred about the structure of reality from those models.

Does the galaxy have dark matter at heart?

The black hole at the centre of our galaxy might actually be a huge blob of dark matter, suggest astrophysicists. A super-dense core of subatomic particles called fermions, spreading out into a vast, diffuse cloud, would match up with observations (and a direct image captured in 2022) equally as well as a black hole, they say. If the Milky Way really is permeated by a cloud of fermionic dark matter — and we’d need better observations to confirm it for sure — it could help to answer outstanding questions about how the whole galaxy behaves.

Clearest gravitational-wave detection yet confirms Hawking’s black-hole theory

Using the Laser Interferometer Gravitational-Wave Observatory (LIGO), researchers have confirmed the late Stephen Hawking’s theorem that the surface area of a black hole can never decrease. Physicists detected the gravitational waves of two black holes fusing together, and later the vibrations produced by the single black hole birthed by the collision. Analysis of this ‘ringdown’ showed that the resulting black hole had a surface area of 400,000 square kilometres — almost double the combined surface area of its parents.

Monster black hole merger is biggest ever seen

The biggest ever merger of colliding black holes involved holes that were too massive to have formed from collapsing stars. And the holes were spinning about 40 times per second — near the limit of what Einstein’s general theory of relativity allows. These ‘forbidden’ high-mass black holes might have been the product of an earlier merger. It’s like “four grandparents merging into two parents merging into one baby black hole”, says physicist Alan Weinstein.

A Spiral Structure in the Inner Oort Cloud

Astronomers discovered a spiral structure in the Oort cloud by chance after data were visualised as part of a planetarium show. Movie-makers at the American Museum of Natural History sourced real-world data for the upcoming ‘Encounters in the Milky Way’, narrated by actor Pedro Pascal. “It’s kind of a freak accident that it actually happened,” said David Nesvorny.

Planet goes out in blaze of glory

Scientists have observed a distant planet plunging into the star it was orbiting, revealing a new way that planets can ‘die’. Physicists first spotted a bright flash from the planet in 2023, which they thought meant it had been engulfed by its host star during end-of-life expansion. When they used the James Webb Space Telescope to take a second look, they found that the star was too early in its life cycle to have started expanding. The team now proposes the planet’s orbit got closer and closer to the star over millions of years, until the two finally collided.

The expanding Universe — do ongoing tensions leave room for new physics?

A century ago, astronomer Edwin Hubble made groundbreaking observations showing that galaxies existed beyond the Milky Way — and they’re receding from Earth. Scientists have since been trying to discover the rate at which the Universe is expanding, known as the Hubble constant. But the most precise measurements of how fast galaxies are moving still don’t agree.

Is dark energy getting weaker?

Fresh data have backed up the discovery that dark energy — the mysterious force that makes galaxies accelerate away from each other — has weakened over billions of years. Until last year, all findings were consistent with dark energy being a ‘cosmological constant’, meaning that the Universe should continue to expand at an increasingly fast rate. The new findings show that the amount of dark energy per cubic metre of space is now around 10% lower than it was 4.5 billion years ago, which means that cosmic expansion is now accelerating less.

Record-breaking neutrino is most energetic ever detected

Astrophysicists have observed the most energetic neutrino ever. The particle — which probably came from a distant galaxy — was spotted by the Cubic Kilometre Neutrino Telescope (KM3NeT) anchored to the floor of the Mediterranean Sea. KM3NeT picks up light emitted by high-energy, electrically charged particles such as muons — which can be produced when high-energy neutrinos smash into Earth’s atmosphere. In early 2023, it detected a muon that carried approximately 120 petaelectronvolts of energy. From the particle’s energy and its near-horizontal trajectory, researchers concluded that it was probably produced by a neutrino more than 20 times more energetic than any seen before.

Strange flashes from ancient galaxy deepen mystery of fast radio bursts

Fast radio bursts (FRBs) — mysterious, millisecond-long flashes of energy — might be even weirder than we thought. Most FRBs are thought to come from magnetars, dead stars that usually form in young galaxies and host powerful magnetic fields. Now, astronomers have traced the origin of an FRB to the edge of an ancient galaxy in which stellar activity has slowed, which provides evidence that at least some FRBs must come from another source.

Early galaxies are too big and too bright

Images from the James Webb Space Telescope are a portal to the past, allowing astrophysicists to study galaxies from the first billion years of the universe. These young galaxies appear bigger and brighter than our current theories about the evolution of the universe say they should be, leaving researchers to debate explanations for how these infant galaxies could have grown up so fast.

Stars hint at an unusual black hole lurking in our Galaxy

Images taken by the Hubble Space Telescope point to an elusive intermediate-size black hole in the star cluster ω Centauri. Midsize black holes occupy the no-man’s land between the ‘super massive’ ones thought to lie at the centre of most galaxies and much smaller ones that have about as much mass as a single large star. So far, most candidates have turned out to be neutron stars upon closer inspection.

Five new ways to catch gravitational waves

Scientists are developing ways to spot those ripples in space-time that are invisible to current gravitational-wave-hunting facilities such as LIGO.

1. Ultra-long waves could be detected over many years by measuring the distance between Earth and stars called pulsars.
2. Telescopes are searching for patterns in the cosmic microwave background that would have been imprinted by gravitational waves in the early universe.
3. Observing atoms as they drop down a 1km-tall pipe could reveal waves coming from black hole collisions.
4. Desktop detectors for speculative high-frequency waves could reveal exotic physics right after the Big Bang.
5. A radical idea for spotting gravity waves involves putting a diamond crystal into quantum superposition — something that has never been demonstrated.

How dwarf galaxies lit up the Universe after the Big Bang

Astronomers have used the James Webb Space Telescope to show that faint miniature galaxies swept away a fog of atomic hydrogen in the early Universe — allowing starlight to shine through the cosmos for the first time. Dwarf galaxies roughly 100 times smaller than the Milky Way triggered the process, known as reionisation.

Giant ‘bubble’ in space could be source of powerful cosmic rays

A turbocharged galactic accelerator could produce the Milky Way’s most powerful cosmic rays. The origin of these ultra-fast particles is hard to pin down because they bounce off magnetic fields, so their flight paths are difficult to follow. To get around the problem, researchers measure particles that are produced when cosmic rays hit interstellar gas and that travel in straight lines. One huge gamma-ray-emitting bubble was detected within a star-forming region in the Cygnus constellation.

Supernova mystery solved

The remains of a supernova that revolutionised modern astrophysics has been confirmed as a neutron star. The event, spotted in 1987, was the closest and brightest supernova observed since 1604, giving astronomers the unprecedented view of how stars die. Now the James Webb Space Telescope has peered through the veil of dust left by the explosion and detected ionised argon and sulphur gas, the signature of an ultradense neutron star.

This new map of the Universe suggests dark matter shaped the cosmos

A reconstruction of nearly 9 billion years of cosmic evolution supports the standard model of cosmology, which suggests that mysterious dark matter is the main factor shaping the Universe’s structure. Astronomers traced the X-ray glow of distant galaxy clusters using the most detailed X-ray map of the sky, captured by the eROSITA space telescope. It allowed them to calculate parameters such as ‘lumpiness’ — how much the total mass of matter has concentrated in the cosmic web at any given time due to gravity, especially that of dark matter.

‘Sci-fi instrument’ will hunt for giant gravitational waves in space

The first experiment to measure gravitational waves from space has been given the go ahead by the European Space Agency. The Laser Interferometer Space Antenna (LISA) will send laser-equipped spacecraft to orbit the Sun in search of gigantic ripples in space-time caused by mergers between supermassive black holes, the spiralling of colliding white-dwarf stars and other events. Construction of the multibillion-euro mission will begin in 2025, with the launch planned for 2035.