Astronomy

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The Moon has inspired poets and artists, musicians and playwrights. The sight of our one and only Moon is familiar to anyone that has ever glanced up at the night time (and sometimes day time sky!) Every so often though, our Moon (note the use of capital ‘M’)is joined by a small asteroid that wanders too close. Astronomers have detected an 11-metre wide asteroid that has the snappy name 2024 PT5 and it came within 567,000 kilometres of Earth and will become a temporary satellite from 29 September until 25 November when it will leave our system. 

Planets, comets, satellites and asteroids are the main constituents of our Solar System, plus of course, the Sun. The asteroids are small rocky objects that orbit the Sun with the majority in orbits between Mars and Jupiter. These remnants of the early Solar System come in a wide range of sizes from those measuring just a few centimetres to others measuring hundreds of kilometres. They have no atmosphere and are usually irregular in shape. 

The asteroid Dimorphos was captured by NASA’s DART mission just two seconds before the spacecraft struck its surface on Sept. 26, 2022. Observations of the asteroid before and after impact suggest it is a loosely packed “rubble pile” object. Credit: NASA/JHUAPL

Asteroids that pass within 1.3 astronomical units (one astronomical unit is the average distance between the Sun and Earth) are typically referred to as near-earth objects (NEOs.) Their proximity to Earth means they may – if not immediately – pose a potential impact threat to Earth. Most NEO’s pass by harmlessly on each orbit but they are tracked for future threats. The study of this family of asteroids helps us to understand about the formation of the Solar System. 

On occasions, Earth can capture asteroids from the NEO group and for a short period, pull them into an orbit. These temporary captures can be very short lived not even lasting for an entire orbit before returning to their regular trajectory.  Others like 2006RH120 remained in orbit around Earth for a year, while some have been captured for more than a year. These mini-moon events have even turned out to be pieces of space junk like one identified in 2020 which turned out to be a rocket booster from the launch of Surveyor 2 in 1966!

This 1964 photograph shows a Centaur upper-stage rocket before being mated to an Atlas booster. A similar Centaur was used during the launch of Surveyor 2 two years later. Credit: NASA

Asteroid 2024 PT5 is a NEO that was discovered on 7 August 2024 by ATLAS, the Asteroid Terrestrial-impact Last Alert System. It measures 11 metres across and can approach within 1 million kilometres of Earth in an orbit whose path resembles a horseshoe shape. This complex type of orbit occurs when a smaller object orbits a relatively larger object. In the case of 2024 PT5, the gravitational attraction of Earth changes the shape of the asteroids elliptical orbit. The horseshoe shape is only evident when the orbit of the asteroid is mapped relative to both the Sun and the Earth.

The dynamics of the two objects means that for a period of 56 days from 29 September to 25 November, 2024 PT5 will officially orbit the Earth although it is only classed as a ‘temporary captured flyby.’ It will only perform one single orbit however before it returns to its usual heliocentric, Sun centred orbit. This won’t be the only time though as it is predicted to return again in 2055. 

Don’t get too excited about seeing it though. The object will be far too faint to be seen with the naked eye, even beyond the visual range of amateur telescopes. It is however possible for experienced amateur astronomers to capture images of the asteroid using astronomical imaging techniques.

Source : A Two-month Mini-moon: 2024 PT5 Captured by Earth from September to November

The post Earth Will Have a Tiny New Mini-Moon for a Few Months appeared first on Universe Today.

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When the James Webb Space Telescope was launched on Christmas Day in 2021, it faced a whole host of intriguing questions. By the time it finally launched, astronomers had a big list of targets begging for the type of detailed observations that only the powerful infrared space telescope could perform. One of the targets was an ancient, massive galaxy that’s basically dead and forms no new stars.

The results are in, and an international team of astronomers know what happened to the quiescent galaxy.

The growth and evolution of galaxies is a key field of study in astronomy. How did we get from the Big Bang to today, when massive galaxies like our own Milky Way populate the Universe? Astronomers have learned that supermassive black holes (SMBHs) reside at the heart of massive galaxies and have shaped their galaxies in powerful ways.

SMBHs create powerful active galactic nuclei (AGN) in galaxies’ cores. As an SMBH draws material toward it, the material collects in an accretion disk. The material is heated to extremely high temperatures and gives off energy across the electromagnetic spectrum, creating an AGN that can outshine the rest of the galaxy.

AGN are powerful objects. According to theory, they have the power to disrupt the supply of cold star-forming gas and to dramatically slow the star formation rate (SFR) in their host galaxy. They blow winds of star-forming gas out of their galaxies, which slows the SFR. Astronomers call this quenching, and it’s frequently observed in massive galaxies called quiescent galaxies.

Now, the JWST has observed an ancient massive galaxy named GS-10578 at redshift z?=?3.064. It’s nicknamed ‘Pablo’s Galaxy,’ and for such an early stage in the Universe’s evolution, it’s massive: it holds about two billion solar masses. But Pablo’s Galaxy is quenched, meaning most of its star formation happened between 12.5 and 11.5 billion years ago. Many local massive galaxies are quenched, which helped propel the development of the theory of AGN quenching.

A team of scientists has presented their research into Pablo’s Galaxy in a new paper titled “A fast-rotator post-starburst galaxy quenched by supermassive black-hole feedback at z?=?3.” The paper is published in Nature Astronomy, and the co-lead author is Francesco D’Eugenio from the Kavli Institute for Cosmology and the Cavendish Laboratory at the University of Cambridge in the UK.

“We found the culprit. The black hole is killing this galaxy and keeping it dormant, by cutting off the source of ‘food’ the galaxy needs to form new stars.”

Francesco D’Eugenio, Kavli Institute for Cosmology, University of Cambridge, UK

“Local, massive, quiescent galaxies stand like colossal wrecks of glorious but remote star-formation histories (SFHs) and mighty and rapid quenching, the likes of which have no present-day equals,” the authors write. “The James Webb Space Telescope (JWST) has enabled us for the first time to witness these monumental galaxies during the long-gone epoch when they arose and fell.”

“Based on earlier observations, we knew this galaxy was in a quenched state: it’s not forming many stars given its size, and we expect there is a link between the black hole and the end of star formation,” said co-lead author Dr Francesco D’Eugenio from Cambridge’s Kavli Institute for Cosmology. “However, until Webb, we haven’t been able to study this galaxy in enough detail to confirm that link, and we haven’t known whether this quenched state is temporary or permanent.”

“In the early universe, most galaxies are forming lots of stars, so it’s interesting to see such a massive dead galaxy at this period in time,” said co-author Professor Roberto Maiolino, also from the Kavli Institute for Cosmology. “If it had enough time to get to this massive size, whatever process that stopped star formation likely happened relatively quickly.”

Pablo’s Galaxy is sometimes called a ‘blue nugget,’ a class of galaxies thought to exist only in the early Universe. Blue nuggets are massive and extremely compact, and astronomers think they’re precursors to modern quiescent galaxies called ‘red nuggets.’ Blue nuggets are experiencing ‘gas-rich compaction.’ That means that there’s a central burst of star formation that’s driven by disk instability or gas-rich major mergers. That burst is followed by quenching, which leaves a red nugget galaxy.

Artist’s illustration of a “red nugget” galaxy. Credits: X-ray: NASA/CXC/MTA-Eötvös University/N. Werner et al., Illustration: NASA/CXC/M. Weiss

“As we will show, GS-10578 is, instead, already a red nugget in an advanced stage of quenching,” the authors write. They explain that it’s merging with several low-mass satellite galaxies and “is undergoing powerful, ejective feedback from its SMBH.”

The researchers say they’ve direct evidence that AGN feedback can quench star formation in early galaxies. Previous observations with other telescopes show that galaxies have fast outflowing winds of gas. That gas is hot, making it easier to see, but it didn’t provide evidence that SMBHs and AGN can quench star formation. That’s because the gas is hot, and stars form from cold, dense gas.

Pablo’s Galaxy is no different. It’s expelling large quantities of hot gas at velocities high enough to escape the galaxy completely. The SMBH and its AGN are pushing the gas out.

But the JWST made the difference in these new observations. It observed a new component of the outflowing wind made of cold gas. The cold gas doesn’t emit light, but the JWST is extremely sensitive and can detect it by the way it blocks out light from distant galaxies in the background. Critically, without cold gas, a galaxy struggles to form stars and becomes quenched.

This figure illustrates some of the research findings. It shows Pablo’s Galaxy in the middle, with five low-mass satellite galaxies merging. The inset (b) shows detail from the main image. The cyan outline is offset to the northwest and represents the outflow of cold gas that is quenching star formation in the galaxy. Image Credit: D’Eugenio and Maiolino et al. 2024.

The amount of gas being expelled by the AGN-driven winds is greater than the amount needed to form new stars.

“We found the culprit,” said D’Eugenio. “The black hole is killing this galaxy and keeping it dormant, by cutting off the source of ‘food’ the galaxy needs to form new stars.”

These are exciting results, but the authors caution that this is just one galaxy. “GS-10578 represents a unique opportunity to study how the most massive galaxies in the Universe became—and stayed—quiescent,” the authors explain in their research. “Even though we cannot draw general conclusions from a single target, we show that AGN feedback is capable of powering neutral-gas outflows with high velocity and high mass loading, sufficient to interrupt star formation by removing its cold-gas fuel.”

There are also still outstanding questions. Other galaxies similar to Pablo’s Galaxy also show that outflow winds of cold gas could be key to galaxies’ quenching. “How exactly these outflows are coupled with the AGN is not yet clear,” the authors write. They explain that only a census of similar galaxies can tell us whether these strong ejections of star-forming gas are a key mechanism for causing quenching or if the ejection of gas is merely episodic.

The JWST also answered another outstanding question about quenched galaxies. Our theoretical models showed that when a galaxy’s star formation was quenched, it was a turbulent event that violently destroyed the galaxy’s shape. Pablo’s Galaxy still displays the stately disk-shape of an untroubled galaxy. Its stars are moving in a uniform, predictable way.

This figure from the study shows the Pablo Galaxy’s orderly rotation. The observed velocity difference is because one side is moving away from us and is red-shifted from our perspective, while the other is moving toward us and is blue-shifted. Image Credit: D’Eugenio and Maiolino et al. 2024.

The JWST is working exactly as intended. By bringing the ancient Universe into view, it’s answering many longstanding questions in astronomy, astrophysics, and cosmology.

“We knew that black holes have a massive impact on galaxies, and perhaps it’s common that they stop star formation, but until Webb, we weren’t able to directly confirm this,” said Maiolino. “It’s yet another way that Webb is such a giant leap forward in terms of our ability to study the early universe and how it evolved.”

The post A Black Hole has Almost Halted Star Formation in its Galaxy appeared first on Universe Today.

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