Astronomy

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Neutron stars are as dense as the nucleus of an atom. They contain a star’s worth of matter in a sphere only a dozen kilometers wide. And they are light-years away. So how can we possibly understand their interior structure? One way would be to simply spin it. Just spin it faster and faster until it reaches a maximum limit. That limit can tell us about how neutron stars hold together and even how they might form. Obviously, we can’t actually spin up a neutron star, but it can happen naturally, which is one of the reasons astronomers are interested in these maximally spinning stars. And recently a team has discovered a new one.

All neutron stars rotate on their axes. They form from the collapse of a massive star’s core, and just as an ice skater spins faster as they pull in their arms, a neutron star spins up as it forms. Young neutron stars can rotate hundreds of times a second, though they generally slow down as they age. Interactions between their magnetic fields and interstellar space cause their rate of rotation to decay. This is why, for example, we can observe pulsars gradually slow down over time.

But many neutron stars have a binary companion. If their companion happens to be a closely orbiting regular star, the neutron star can pull off some of the companion’s outer layer and capture it. The slow exchange of matter can cause the neutron star to speed up as it essentially steals some of the orbital angular momentum of the companion. They are known as millisecond pulsars because they emit a radio pulse every few milliseconds. They are the fastest-rotating stars in the cosmos.

So, just how fast can these neutron stars spin? The record for the fastest spinning pulsar is held by PSR J1748–2446ad. Observations in 2004 and 2005 confirmed it rotates 716 times per second. That’s a bit faster than number two, which rotates at 707 times a second. This new study has found another neutron star rotating at 716 times a second, and it’s interesting because it isn’t a pulsar.

X-ray burst showing the 716 Hz oscillation. Credit: Jaisawal, et al

Known as 4U 1820-30, it is part of a binary X-ray system. As the neutron star captures material from its companion, part of its surface will heat up to such a degree that it emits X-rays. As the neutron star rotates, the hot-spot swings in and out of view, and we observe a periodic pulsation of X-rays. Using NASA’s NICER X-ray telescope, the team observed the binary from 2017 to 2021 and captured data on 15 powerful X-ray bursts. One of these bursts had a clear periodicity of 716 Hz. This strongly suggests the neutron star rotates at that rate.

While it could just be a statistical fluke, the fact that we now have two 716 Hz neutron stars found in two different ways suggests they may be near the maximal rotation limit for a neutron star.

Reference: Jaisawal, Gaurava K., et al. “A Comprehensive Study of Thermonuclear X-Ray Bursts from 4U 1820–30 with NICER: Accretion Disk Interactions and a Candidate Burst Oscillation.” The Astrophysical Journal 975.1 (2024): 67.

The post Astronomers Have Found the Fastest Spinning Neutron Star appeared first on Universe Today.

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Carbon is the building block for all life on Earth and accounts for approximately 45–50% of all dry biomass. When bonded with elements like hydrogen, it produces the organic molecules known as hydrocarbons. When bonded with hydrogen, oxygen, nitrogen, and phosphorus, it produces pyrimidines and purines, the very basis for DNA. The carbon cycle, where carbon atoms continually travel from the atmosphere to the Earth and back again, is also integral to maintaining life on Earth over time.

As a result, scientists believe that carbon should be easy to find in space, but this is not always the case. While it has been observed in many places, astronomers have not found it in the volumes they would expect to. However, a new study by an international team of researchers from the Massachusetts Institute of Technology (MIT) and the Harvard-Smithsonian Center for Astrophysics (CfA) has revealed a new type of complex molecule in interstellar space. Known as 1-cyanoprene, this discovery could reveal where the building blocks of life can be found and how they evolve.

The research was led by Gabi Wenzel, a postdoctoral researcher from the Department of Chemistry at MIT. She was joined by researchers from the CfA, the University of British Columbia, the University of Michigan, the University of Worchester, the University of Virginia, the Virginia Military Institute (VMI), the National Science Foundation (NSF), the National Radio Astronomy Observatory (NRAO), and the Astrochemistry Laboratory at NASA’s Goddard Space Flight Center (GSFC). The paper that describes their findings recently appeared in the journal Science.

Artist’s impression of complex organic molecules in space. Credit: NSF/NSF NRAO/AUI/S. Dagnello

For their study, the team relied on the NSF Green Bank Telescope (GBT), the most accurate, versatile, and largest fully-steerable radio telescope in the world, located at the Green Bank Observatory in West Virginia. This sophisticated instrument allowed the team to detect the presence of 1-cyanopyrene based on its unique rotational spectrum. 1-cyanoprene is a complex molecule composed of multiple fused benzene rings and belongs to the polycyclic aromatic hydrocarbon (PAHs) class of molecules. On Earth, they are created by burning fossil fuels or other organic materials, like charred meat or burnt bread.

By studying PHAs, astronomers hope to learn more about their lifecycles and how they interact with the ISM and nearby celestial bodies. As co-author Harshal Gupta, the NSF Program Director for the GBO and a Research Associate at the CfA, explained in a recent CfA press release:

“Identifying the unique rotational spectrum of 1-cyanopyrene required the work of an interdisciplinary scientific team. This discovery is a great illustration of synthetic chemists, spectroscopists, astronomers, and modelers working closely and harmoniously.”

This was an impressive feat due to the difficulty (or even impossibility) of detecting these molecules due to their large size and lack of a permanent dipole moment. “These are the largest molecules we’ve found in TMC-1 to date. This discovery pushes the boundaries of our understanding of the complexity of molecules that can exist in interstellar space,” added co-author MIT professor Brett McGuire, who is also an adjunct astronomer at the NSF and the NRAO.

Previously, these molecules were believed to form only in high-temperature environments, like the region surrounding older stars. This concurs with what astronomers have known for a long time about certain carbon-rich stars, which produce massive amounts of small molecular sheets of carbon that they then distribute into the interstellar medium (ISM). In addition, previous research has suggested that the infrared fluorescence of PAHs – caused by the absorption of ultraviolet radiation from nearby stars – could be responsible for infrared bands observed in many celestial objects.

Artist’s impression of Green Bank Telescope conducting radio astronomy with the help of AI algorithms. Credit: Breakthrough Listen/Danielle Futselaar.

The intensity of these bands has led some astronomers to theorize that PAHs could account for a significant fraction of carbon in the ISM. Other astronomers have maintained that these carbon-rich molecules could not survive the harsh conditions of interstellar space because temperates in the ISM are far too low – averaging about 10 K (-263 °C; -442 °F). However, the 1-cyanopyrene molecules Wenzel and her colleagues observed were located in the nearest star-forming region to Earth, the cold interstellar cloud known as Taurus Molecular Cloud-1 (TMC-1).

Since this Nebula has not yet started forming stars, its temperature is the same as that of the ISM. “TMC-1 is a natural laboratory for studying these molecules that go on to form the building blocks of stars and planets,” said Wenzel. These observations suggest that PHAs like 1-cyanopyrene may have a different formation mechanism entirely and/or can survive the harsh environment of space. In the meantime, detecting cyanopyrene can provide indirect evidence of even larger and more complex molecules in future observations. 

This research was supported by measurements and analysis conducted by the molecular spectroscopy laboratory of Dr. Michael McCarthy at the CfA. As he indicated:

“The microwave spectrometers developed at the CfA are unique, world-class instruments specifically designed to measure the precise radio fingerprints of complex molecules like 1-cyanopyrene. Predictions from even the most advanced quantum chemical theories are still thousands of times less accurate than what is needed to identify these molecules in space with radio telescopes, so experiments in laboratories like ours are indispensable to these ground-breaking astronomical discoveries.”

Further Reading: CfA

The post Astronomers Discover Potential New Building Block of Organic Matter in Interstellar Space appeared first on Universe Today.

What if a rocket could return to its launch tower -- and be caught?

The Solar System’s hundreds of moons are like puzzle pieces. Together, they make a picture of all the forces that can create and modify them and the forces that shape our Solar System. One of them is Miranda, one of 28 known moons that orbit the ice giant Uranus. Miranda is its smallest major moon, at 471 km in diameter.

New research shows that this relatively small, distant moon may be hiding something: a subsurface ocean.

Miranda stands out from the other moons for one reason: its surface is a bizarre patchwork of jumbled terrain. There are cratered areas, rough scarps, and grooved regions. It may have the tallest cliff in the Solar System, a 20 km drop named Verona Rupes. Many researchers think its surface is deformed by tidal heating from gravitational interactions with some of the Uranus’ other moons.

New research in The Planetary Journal set out to explain Miranda’s jumbled geology. It’s titled “Constraining Ocean and Ice Shell Thickness on Miranda from Surface Geological Structures and Stress Modeling.” The lead author is Caleb Strom, a graduate student at the University of North Dakota.

“To find evidence of an ocean inside a small object like Miranda is incredibly surprising,”

Tom Nordheim, co-author and planetary scientist at the Johns Hopkins Applied Physics Laboratory

Scientists don’t have much to go on when it comes to Miranda. The only spacecraft to image it was Voyager 2 in 1986. Even then, the flyby was brief, and the spacecraft only imaged the moon’s southern hemisphere. But that was enough to reveal the moon’s bizarre and complex geological surface features. Miranda’s strange surface coronae attracted a lot of attention.

This figure from the study shows some of Miranda’s surface features. The moon is known for its coronae features, two of which are labelled here. Image Credit: Strom et al. 2024.

When the images were first received, scientists were baffled by Miranda’s complexity. Some called it a “patchwork planet,” and there was much healthy speculation about what created it. Attempts to understand the moon are still limited by the amount of data that Voyager 2 provided. However, modern scientists have access to a more powerful tool than scientists did in the 80s: computer models and simulations.

Strom and his co-researchers used a computer model to work backward from Miranda’s current surface. They started by mapping Miranda’s surface features, including its cracks, ridges, and unique trapezoidal coronae, and then reverse-engineered it. They tested different models of the moon’s interior to see what could account for the varied surface.

This simple schematic shows the four-layer model Strom and his co-researchers worked with. Image Credit: Strom et al. 2024.

The model that best matched the surface was one where Miranda had a vast ocean under its surface some 100-500 million years ago. The icy crust is probably 30 km thick or less, and the ocean could be up to 100 km thick.

“Our results show that a thin crust (?30 km) is most likely to result in sufficient stress magnitude to cause brittle failure of ice on Miranda’s surface,” the authors explain in their research. “Our results also suggest the plausible existence of a ?100 km thick ocean on Miranda within the last 100–500 million yr.”

“To find evidence of an ocean inside a small object like Miranda is incredibly surprising,” said Tom Nordheim, a planetary scientist at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, a study co-author, and the principal investigator on the project that funded the study. “It helps build on the story that some of these moons at Uranus may be really interesting — that there may be several ocean worlds around one of the most distant planets in our solar system, which is both exciting and bizarre.”

Tidal heating is responsible for this, and it came from gravitational relationships between Miranda and Uranus’ other moons. Moons tug on each other, and when they’re in an orbital resonance with one another, where each moon’s period around a planet is an exact integer of the others’ periods, those tugs are amplified. These forces can periodically deform the moons, and as they’re squeezed, they heat up, keeping subsurface oceans warm and liquid.

Miranda and other moons of Uranus were likely in resonance in the past, which could’ve created surface fractures and related terrain.

A digital elevation model (DEM) of Miranda’s Inverness Coronae. The relative elevation ranges from 0 km (purple) to 4 km (red). Image Credit: Beddingfield et al. 2022.

However, resonances don’t last forever, and the researchers think that some time ago, Miranda left orbital resonance, and its interior began to cool. They don’t think it’s completely cooled yet because if the ocean had completely frozen, it would’ve expanded and displayed telltale surface cracks. So, the interior ocean likely still exists but is probably much thinner than in the past. “But the suggestion of an ocean inside one of the most distant moons in the solar system is remarkable,” Strom said.

Nobody predicted that Miranda would have an ocean. As far as scientists could tell, it was a frozen ball. But they’ve been wrong about moons before.

Researchers used to think that Saturn’s moon, Enceladus, the most reflective object in the Solar System, was just a ball of ice. After all, its surface is smooth and clearly frozen solid. However, the Cassini mission showed us that it may not be totally frozen. There’s a bevy of evidence that Enceladus has a warm ocean under a layer of ice.

This false-colour image of the plumes erupting from Enceladus is easily recognizable to many. Enceladus and Miranda are similar in important ways. Could Miranda also be geologically active? Image Credit: NASA/ESA

“Few scientists expected Enceladus to be geologically active,” said co-author Alex Patthoff. “However, it’s shooting water vapour and ice out of its southern hemisphere as we speak.”

Since both Enceladus and Miranda are roughly the same size and may have similar ice shells, it increases the chances that Miranda also has an ocean. Other moons, like Saturn’s Europa, may also be icy ocean moons. Now, scientists think these moons and their warm oceans are the best targets in the search for life in our Solar System.

Other recent research suggests that Miranda could be more like Enceladus than thought. One 2023 study showed that the moon may be releasing material into space like Enceladus does. The ESA and NASA are both sending probes to Jupiter to study Europa and other potential ocean moons. Should we expand that search to distant Uranus and its small moon Miranda?

An artist’s impression of Uranus and its five largest moons (innermost to outermost): Miranda, Ariel, Umbriel, Titania and Oberon. A 2023 paper showed that Ariel and/or Miranda could be releasing material into space. Image Credit: NASA/Johns Hopkins APL/Mike Yakovlev

“We won’t know for sure that it even has an ocean until we go back and collect more data,” said study co-author Nordheim. “We’re squeezing the last bit of science we can from Voyager 2’s images. For now, we’re excited by the possibilities and eager to return to study Uranus and its potential ocean moons in depth.”

For now, all we have is decades-old Voyager 2 data. However, the data and the computer models the team employed shed new light on Miranda.

“We interpret the tidal stress model results to indicate that at some point in Miranda’s geologic past, it experienced an intense heating event that resulted in a thin crust (?30 km). Such a thin crust would also have resulted in a ?100 km thick ocean to account for the molten part of the hydrosphere. This thin ice crust and thick ocean could have allowed for intense tidal stress leading to significant geologic deformation in the form of brittle deformation at Miranda’s surface,” the authors explain.

“In conclusion, our results suggest that Miranda could have had a subsurface ocean in the geologically recent past from an intense heat pulse, consistent with dynamical modelling results of previous studies,” they conclude.

The post There’s Another Ocean Moon Candidate: Uranus’ Tiny Moon Miranda appeared first on Universe Today.