Category: Astronomy

A Japanese astrophysicist has reported a faint but unusually sharp gamma-ray glow around the Milky Way, based on 15 years of data from NASA’s Fermi telescope. The signal peaks near 20 GeV, forms a round halo, and closely matches what researchers expect from dark matter. The result has renewed interest in one of physics’ biggest open questions.

Tomonori Totani studied a wide region around the galaxy while masking the bright central plane. He modeled all known gamma-ray sources and removed them from the data. What remained was a smooth, spherical excess centered on the Milky Way that did not match any familiar process.

The shape and energy peak stand out because most gamma-ray sources follow broad trends. This signal rises from a few GeV, peaks sharply at 20 GeV, and fades above 100 GeV. That pattern resembles the expected signature from dark matter particles that collide and produce ordinary particles. A 20 GeV peak would point to particles weighing about 500 to 800 GeV.

Totani reported a significance above 15 sigma and tested many ways to remove the signal, including changes to cosmic-ray models, the Fermi bubble outlines, and masking choices. The excess stayed in every test.

Alternative explanations exist but do not fit as well. Millisecond pulsars can explain a known excess near the galactic center, but they would not produce a large spherical halo. Cosmic-ray activity could mimic some energy features but would usually show signs of the disk. The inverse-Compton process comes closest but does not match the symmetry.

If the excess is from dark matter, the numbers suggest particles around 600 GeV with an interaction rate higher than simple models predict. This pushes against limits from dwarf galaxies but is not ruled out.

The signal also differs from the lower-energy excess at the galactic center, which many researchers now link to faint pulsars. The two features likely have separate origins.

More data will be needed to confirm or reject the dark matter idea. Ground-based gamma-ray telescopes and neutrino observatories can check for related signals. Fermi will also continue collecting data that may clarify whether the halo glow marks the long-awaited trace of dark matter.

Source: 20 GeV halo-like excess of the Galactic diffuse emission and implications for dark matter annihilation

A research team using data from the Dark Energy Spectroscopic Instrument in Arizona has identified seven new quasar systems that appear to act as gravitational lenses. They reported the results this year after training a neural network to scan more than eight hundred thousand quasar spectra.

The work matters because these rare alignments let astronomers measure the masses of quasar host galaxies, which are normally hidden behind the quasar’s strong light. The group built its model by mixing real quasar data with simulated background galaxies, and the method found far more strong candidates than earlier surveys.

Quasars shine when supermassive black holes consume nearby gas and dust. Their light usually hides the galaxies that surround them. In rare cases, a quasar sits in the near-perfect position to bend the light of a more distant galaxy behind it. The closer galaxy’s gravity pulls the background light into our line of sight. This forms what astronomers call a lens, but the bright quasar often hides the pattern in normal images.

These systems are rare because the alignment must be very close to perfect. Large surveys such as the Sloan Digital Sky Survey contain hundreds of thousands of quasars, yet only a small number show clear signs of lensing. Before this study, researchers had confirmed only three systems where the quasar host served as the lens. Several more were possible but needed stronger evidence.

The DESI project collects millions of spectra with a wide-field telescope at Kitt Peak in Arizona. Its early data release included spectra from more than eight hundred thousand quasars. Instead of relying on imaging, the team focused on the spectra. To train the network, they created mock lenses by adding distant galaxy signals to real quasar spectra. This approach gave the model enough examples to learn what a lensed system should look like.

The network searched for extra emission lines at higher redshifts than the quasar’s own features. These lines come from the background galaxy. Ground-based telescopes blend light from close objects into one spectrum, so the background signal can ride along with the quasar’s light. The model looked for these faint features that would normally be lost in the noise.

The system returned seven strong candidates on the first pass. All showed an oxygen line from a more distant galaxy. Four candidates included extra lines from hydrogen and additional oxygen signals. The process also found the one known system in DESI’s footprint, confirming that the method works. This result more than doubled the number of high-quality candidates in the survey area.

These quasars sit at redshifts up to about 1.8, meaning their light began its journey billions of years ago. Some of the background galaxies lie even farther away. In a few cases, the farther sources may sit at redshift 3 or beyond, which places their light in the early universe.

The interest in these lenses goes beyond the alignment. When a quasar host galaxy bends the light of a background galaxy, astronomers can measure the Einstein radius, which relates directly to mass. It gives a clear reading of the host galaxy’s mass, including dark matter, even when the quasar normally blocks the view.

Measuring these masses helps test how galaxies and their central black holes grew together. In the nearby universe, the size of a galaxy and the mass of its black hole follow a close trend. At higher redshifts, quasars are so bright that standard methods cannot separate their host galaxies. Lensing offers a way around that problem.

The new candidates also help scientists study feeding habits of black holes in the early universe. When a quasar lenses an even more distant galaxy, it gives a view of objects that formed when the universe was only a few billion years old. These systems show how matter moved between galaxies at that time.

DESI will expand its survey in future releases. With more spectra and improved training sets, researchers expect many more detections. Space telescopes such as Hubble and the James Webb Space Telescope (JWST) can then take sharp images of the best systems. Those images can confirm the lensing pattern and map the mass in the quasar host galaxy.

The latest study shows how machine learning can raise the discovery rate from rare finds to a steady flow. Seven new strong candidates from one search mark a clear shift in how quickly these systems can be found. As the dataset grows, the list of quasar lenses is expected to grow with it.

Source: Quasars acting as Strong Lenses Found in DESI DR1

Astronomers

have reported that the Pleiades, the bright star cluster seen in the constellation Taurus, is only the compact core of a far larger family of stars that formed together about 125 million years ago. By using data from NASA’s TESS satellite and the European Space Agency’s Gaia spacecraft, researchers identified more than 3,000 related stars spread across nearly 2,000 light-years of space.

The Pleiades, often called the Seven Sisters, has been known for thousands of years. On a clear night, most people can see six or seven bright stars close together in the sky. Astronomers had already studied this central cluster in detail, which lies about 440 light-years from Earth. Until now, the focus remained on only this compact region.

The new research shows that this visible group is just the middle of what scientists now call the Greater Pleiades Complex. Many related stars sit far from the bright core and do not form a tight cluster anymore. Some are hundreds of light-years away, while others lie more than a thousand light-years from the center.

To find these hidden members, scientists tracked how fast stars rotate. Young stars spin faster than older ones, and their spin causes small changes in brightness as dark spots move across their surfaces. TESS measures these tiny shifts in light. Gaia then provides exact positions, distances, and movements through space. By combining these two sets of information, the team found stars that move like the Pleiades and spin at the same youthful rate.

This method revealed long streams of stars that appear to have drifted from the original cluster over time. One stream, called UPK 303, can be traced back toward the Pleiades’ location at the time of its birth. Other groups, such as UPK 545, likely formed in the same large gas cloud but ended up far apart as the cluster slowly broke up.

Most stars form in groups, but gravity and the pull of the Milky Way usually tear these clusters apart within a few hundred million years. The Greater Pleiades Complex shows that even after a cluster spreads out, its members can still be identified by their shared motion and age. This changes how astronomers view the nearby region of space and suggests there may be many more hidden star families around us.

The Pleiades has long been used to study how young stars and planets develop. Adding thousands of stars of the same age gives scientists a much larger sample to compare. This can help improve models of how planets form and how stellar systems change over time.

The study focused on stars between about 50 and 200 million years old, when rotation is still easy to measure. Researchers now plan to use the same approach on other famous groups, including the Hyades and the Scorpius–Centaurus region. The current list includes about 3,100 strong candidates, but future data releases from Gaia and more observations from TESS may reveal many more.

The Sun is not part of this family, but it likely formed in a similar cluster long ago. Studies like this may one day help locate stars that were born alongside our own.

When you look up at the Pleiades on a clear winter night, you are only seeing the bright center. Around it, spread wide across the galaxy, lies a much larger family that began in the same cloud of gas and dust millions of years ago.

Source: Lost Sisters Found: TESS and Gaia Reveal a Dissolving Pleiades Complex

The Moon will reach its greatest distance from Earth in 18 years on November 20, hours before the new moon. Astronomers say the timing of this apogee, which places the Moon about 406,690 kilometers from Earth, creates an unusual mix of weak tides, a smaller lunar appearance, and sky positions that match an 18.6-year cycle of extreme rises and sets.

The event happens early on November 20 around 02:46 UTC, when the Moon moves to the farthest point in its orbit. At this range, radio signals take noticeably longer to travel to the Moon and back compared with regular days. The distance is the highest since 2007 and will not occur again until late 2043.

The Moon travels around Earth in an oval path, so its distance changes from month to month. It comes closest at perigee and farthest at apogee. These distances shift slightly each orbit because the Sun’s gravity pulls on the Moon and slowly changes the shape and direction of its path. When this gradual wobble lines up with Earth’s own position around the Sun, the most distant apogees appear.

This month’s alignment pushes the Moon to one of its most distant points in nearly two decades. Astronomers have been expecting this peak for months because the orbit cycle is well measured and repeats on a predictable schedule.

The apogee arrives during the new moon phase, when the moon sits between Earth and the sun. The side facing us is unlit, so the moon is not visible. New moons usually bring strong tides, but the distance this month weakens them. In many coastal regions, high tides drop by about 10 to 15 centimeters. Low tides can reveal patches of mud and rock that usually stay underwater.

Although no one can see the Moon that day, its size change is noticeable over the month. At this distance, the Moon looks about 14 percent smaller than it does at a close perigee. The area it covers in the sky drops by almost a quarter. Anyone who compares recent photographs of the moon from earlier this month with those taken in December will see the difference.

This distant apogee also connects to the lunar standstill, a cycle that peaks every 18.6 years. During these periods, the Moon rises and sets at its most extreme points in the sky. For many locations in the Northern Hemisphere, moonrises and moonsets drift far to the south right now. Historic sites such as Stonehenge and Callanish were designed to track these extremes, and observers still study them during standstill years.

Most people will not notice anything unusual on November 20 itself because the Moon remains lost in daylight. The best viewing comes in the days after the new moon, when a thin crescent rises very high or low at dawn or dusk. Through binoculars, the Moon appears smaller and sharper than usual, marking this rare point in its long orbital cycle.