Category Archives: Dark Matter

Astronomy, Black Hole, Cosmology, Dark Matter, NASA, Planets

Ten amazing space discoveries in 2024.

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The Early Universe is Running out of Supermassive Black holes.

As the Webb Space Telescope continues to find supermassive blackholes (SMBH) in the time after the Dark Ages, there has been a significant down turn in their masses. Now the most common SMBHs earlier than one billion years ABB are about 4 million solar masses – about the same mass as Sgr A* in our Milky Way.  At 700 million years ABB, Webb found a SMBH with 40 million solar masses. GN-z11 at 420 million years ABB has an estimated mass of 2 million suns. LID-568 (See NASA artwork above) has a mass of 10 million suns at an age 1.5 billion years ABB. ZS7 consists of two merging SMBHs each with a mass of about 50 million suns at an age of about 740 million years ABB. So, Webb is now giving us a glimpse of black hole mergers and rapid growth long before we reach the billion-sun masses of todays SMBHs.

Cosmic Gravity Wave Background

Teams of scientists worldwide have reported the discovery of the “low pitch hum” of these cosmic ripples flowing through the Milky Way. The detected signal is compelling evidence and consistent with theoretical expectations of gravity wave pulses from millions of distant binary hole mergers, where these black holes are of the SMBH variety. The artwork above is provided by NASA. [UC Berkeley News]

DESI survey of 6 million galaxies validates Big Bang

Researchers used the Dark Energy Spectroscopic Instrument (DESI) to map how nearly 6 million galaxies cluster across 11 billion years of cosmic history as shown in the image above (Credit: D. Schlegel/Berkeley Lab using data from DESI). Their observations line up with what Einstein’s theory of general relativity predicts. Looking at galaxies and how they cluster across time reveals the growth of cosmic structure, which lets DESI test theories of modified gravity – an alternative explanation for our universe’s accelerating expansion. DESI researchers found that the way galaxies cluster is consistent with our standard model of gravity and the predictions from Einstein’s theory of general relativity. There is even a suggestion in the data that Dark Energy is weakening as the universe ages over the last 11 billion years. This has huge implications for modeling the future of the universe. [News from Berkeley Lab]

Supersymmetry searches still come up empty-handed

Before the beginning of the Large Hadron Collider data taking, supersymmetry (SUSY)  was seen as a single answer to many unresolved open questions of the Standard Model. The LHC ATLAS research program has first quickly excluded most of the simplest SUSY configurations, then moved to a detailed work targeting many signatures, not necessarily favored by a theoretical prejudice. The lack of an identified SUSY signal so far at the massive ATLAS detector shown above (Credit: ATLAS Experiment © 2022 CERN) is certainly a disappointing and possibly somewhat surprising outcome to many scientists. A lot of theoretical effort into String theory and the search for a quantum theory of gravity hinges on going beyond the so-called Standard Model, and supersymmetry is a key mathematical ingredient to many of these simpler extensions. [LHC-ATLAS Consortium]

Dark Matter searches still find no candidate particles

After 40 years of searching for dark matter candidate particles, the currently most popular assumption for the nature of DM still is that of a (new) particle, even though the jury is not entirely out on whether the present observations of DM are due to a particle (or wave-like behavior at very low masses) or due to our limited understanding of the gravitational force at large scales. The figure above shows the current list of candidate particles being considered (Credit: CERN/G. Bertone and T. M. P. Tait) Despite its success, the Standard Model of particle physics (SM) in its present form (6 quarks, 6 leptons, 1 Higgs boson, plus the 12 quanta for the three non-gravity forces) is not able to offer an explanation for dark matter. It offers no known particle that can play that role. The LHC experiments, meanwhile, have by now completed and published all their main DM search analyses for the Run-2 data taken before 2016. No evidence as yet has been found for signals of the production of dark matter or dark sector particles. Dark matter, as a particle representing some 25% of all gravitating ‘stuff’ in the universe, remains one of the biggest puzzles in physics today.

Origin of the solar wind discovered

After several decades of theoretical speculation, solar physicists are now certain that they have discovered how our sun produces the interplanetary wind of matter that streams out of its corona at speeds of over 200 km/s. In 2024, the ESA-led Solar Orbiter spacecraft made the first ever connection between measurements of the solar wind around a spacecraft to high-resolution images of the Sun’s surface at a close distance. The spacecraft passed through the magnetic field connected to the edge of a coronal hole complex. This let the team watch the way the solar wind changed its speed – from fast to slow or vice versa – and other properties, confirming that they were looking at the correct region. In the end, they got a perfect combination of both types of features together. The image above (Credit:ESA & NASA/Solar Orbiter/EUI Team; acknowledgement: Lakshmi Pradeep Chitta, Max Planck Institute for Solar System Research) taken by the ESA/NASA Solar Orbiter spacecraft shows a ‘coronal hole’ near the Sun’s south pole. Subsequent analysis revealed many tiny jets of plasma being released into the corona and solar wind during the observation. 

The origin of the springtime, dinosaur-killer asteroid

According to a recent article published in Nature magazine, the object that smashed into Earth and kick-started the extinction that wiped out almost all dinosaurs 66 million years ago was an asteroid that originally formed beyond the orbit of Jupiter, according to geochemical evidence from the impact site in Chicxulub, Mexico. Comparisons between the chemical record left behind by the strike 66 million years ago and known meteorite samples suggest that the Cretaceous asteroid was a carbonaceous chondrite. This type of asteroid is one of the oldest known, having formed billions of years ago in the early solar system. As these chondrites can only come from asteroids found beyond Jupiter, it suggests that the asteroid must have had its origins there too. Some of the chondritic spherules got into the gills of dying fish, fossils of which have been used to reveal that  the asteroid impacted during the springtime in the northern hemisphere. This is possible to know based on where the lines of growth in the fish’s bones stop, which can be read somewhat like rings in a tree trunk.

Current round-up of fireball detections worldwide

The most recent world map of detected fireballs from 1988 to 2024 detected with a variety of sensors (optical, infrasound, etc) reveals that fireballs delivering less than 30 kilotons-equivalent TNT upon atmospheric detonation are uniformly spread around Earth’s surface. In 2019 it was determined that the Geostationary Lightning Mapper (GLM) instruments on GOES weather satellites can detect fireballs and bolides. This largely removes much of the observer-bias from the detections irrespective of geographic latitude. The bright red dot is the 2013 Chelyabinsk Meteor fireball and impact. (Credit: NASA/CNEOS/JPL)

NASA spacecraft detects subterranean Martian water

Using seismic activity to probe the interior of Mars, geophysicists have found evidence for a large underground reservoir of liquid water — enough to fill oceans on the planet’s surface. The data from NASA’s Insight lander (2018-2022) allowed the scientists to estimate that the amount of groundwater could cover the entire planet to a depth of between 1 and 2 kilometers, or about a mile. While that’s good news for those tracking the fate of water on the planet after its oceans disappeared more than 3 billion years ago, the reservoir won’t be of much use to anyone trying to tap into it to supply a future Mars colony. It’s located in tiny cracks and pores in rock in the middle of the Martian crust, between 11.5 and 20 kilometers (7 to 13 miles) below the surface. Even on Earth, drilling that deep would be a challenge. [UC Berkeley News].

Organized magnetic fields in Sgr A* black hole accretion disk

A new image from the Event Horizon Telescope (EHT) collaboration has uncovered strong and organized magnetic fields spiraling from the edge of the supermassive black hole Sagittarius A* (Sgr A*). Seen in polarized light for the first time, this new view of the monster lurking at the heart of the Milky Way Galaxy has revealed a magnetic field structure strikingly similar to that of the black hole at the center of the M87 galaxy, suggesting that strong magnetic fields may be common to all black holes. This similarity also hints toward a hidden jet in Sgr A*.Scientists unveiled the first image of Sgr A*— which is approximately 27,000 light-years away from Earth— in 2022, revealing that while the Milky Way’s supermassive black hole is more than a thousand times smaller and less massive than M87’s, it looks remarkably similar. This made scientists wonder whether the two shared common traits outside of their looks. To find out, the team decided to study Sgr A* in polarized light. Previous studies of light around M87* revealed that the magnetic fields around the black hole giant allowed it to launch powerful jets of material back into the surrounding environment. Building on this work, the new images have revealed that the same may be true for Sgr A*. [Credit EHT Collaboration]

Cosmology, Dark Matter, Gravity, Physics

Exactly how many stars are in the Milky Way ?

Based on tons of scientific data and decades of research, here is an artist’s impression of the Milky Way Galaxy, as seen from above the galactic “North pole”. (Credit: NASA. JPL-Caltech/R. Hurt (SSC/Ca)

All of the basic elements have been established including its spiral arm pattern and the shape of its central bulge of stars. To directly answer this question, however, is a difficult, if not impossible, task. The problem is that we cannot directly see every star in the Milky Way because most are located behind interstellar clouds from our vantage point in the Milky Way. The best we can do is to figure out the total mass of the Milky Way, subtract the portion that is contributed by interstellar gas and dust clouds ( about 1 – 5 percent or so), and then divide the remaining mass by the average mass of a single star.

From a number of studies, the mass of the Milky Way inside the orbit of our sun can be estimated to an accuracy of perhaps 20 percent as 140 billion times the mass of the Sun, if you use the Sun’s speed around the core of the galaxy. Radio astronomers have detected much more material outside the orbit of the Sun, so the above number is probably an underestimate by a factor of 2 to 5 times in mass alone.

Now, to find out how many stars this represents, you have to divide by the average mass of a star. If you like the sun, then use ‘one solar mass’ and you then get about 140 billion sun-like stars for what’s inside the sun’s orbit. But astronomers have known for a long time that stars like the sun in mass are not that common. Far more plentiful are stars with half the mass of the sun, and even one tenth the mass of the sun. The problem is that we don’t know exactly how much of the Milky Way is in the form of these low-mass stars. In text books, you will therefore get answers that range anywhere between a few hundred billion and as high as a trillion stars depending on what the author used as a typical mass for the most abundant type of star. This is a pretty embarrasing uncertainty, but then again, why would you need to know this number exactly?

The best estimates come from looking at the motions of nearby galaxies such as a recent study by G. R. Bell (Harvey Mudd/USNO Flagstaff), S. E. Levine (USNO Flagstaff):

Using radial velocities and the recently determined proper motions for the Magellanic Clouds and the dwarf spheroidal galaxies in Sculptor and Ursa Minor, we have modeled the satellite galaxies’ orbits around the Milky Way. Assuming the orbits of the dwarf spheroidals are bound, have apogalacticon less than 300 kpc, and are of low eccentricity, then the minimum mass of our galaxy contained within a radius of 100 kpc is 590 billion solar masses, and the most likely mass is 700 billion. These mass estimates and the orbit models were used to place limits on the possible maximum tangential velocities and proper motions of the other known dwarf spheroidal galaxies and to assess the likelihood of membership of the dwarf galaxies in various streams.

Again, you have to divide this by the average mass of a star…say 0.3 solar masses, to get an estimate for the number of stars which is well into the trillions!

Another factor that confuses the problem is that our Milky Way contains a lot of dark matter that also produces its own gravity and upsets the estimates for actual stellar masses. Our galaxy is embedded in a roughly spherical cloud of dark matter. Various theoretical calculations show that these should be very common among galaxies. Here is an example of such a model in which the luminous galaxy is embedded in a massive DM halo. (Credit:Wikipedia-Dark Matter Halo N-body simulation)

By using the motions of distant galaxies astronomers have ‘weighed’ the entire Milky Way and deduce that the dark matter halo is likely to include around 3 trillion solar masses of dark matter.