Tag: space exploration

Scientists from the University of Warwick have found that our solar system might be pulled into the gravity of a white dwarf star.

The team have helped to answer what happens to planetary systems, like our solar system, when their host stars become white dwarfs.

White dwarfs are the end state of stars when they have burned all their fuel. They can offer insight into different aspects of star formation and evolution.

In the study, the team examined the fate of asteroids, moons, and planets that pass close to the white dwarfs by analysing transits – dips in the brightness of stars caused by objects passing in front of them.

Unlike the predictable transits caused by orbiting planets around stars, transits caused by debris are oddly shaped and disorderly. This suggests the fate of these bodies to be extremely violent.

Dr Amornrat Aungwerojwit of Naresuan University, who led the study, said: “Previous research had shown that when asteroids, moons and planets get close to white dwarfs, the huge gravity of these stars rips these small planetary bodies into smaller and smaller pieces.”

Collisions between these pieces grind them into dust, which finally falls into the white dwarf. This allows the researchers to determine what type of material the original planetary bodies were made from.

The study is published in the Monthly Notices of the Royal Astronomical Society.

The team investigated the changes in the brightness of stars

In the new research, scientists investigated changes in the brightness of stars for 17 years to gather insight into how these bodies are disrupted. They focused on three different white dwarfs which all behaved very differently.

Professor Boris Gaensicke, Department of Physics, University of Warwick, commented: “The simple fact that we can detect the debris of asteroids, maybe moons or even planets whizzing around a white dwarf every couple of hours is quite mind-blowing, but our study shows that the behaviour of these systems can evolve rapidly, in a matter of a few years.

“While we think we are on the right path in our studies, the fate of these systems is far more complex than we could have ever imagined.”

White dwarf’s studied by the team

The first white dwarf (ZTF J0328−1219) studied appeared steady over the last few years. However, the authors found evidence of a major catastrophic event around 2010.

Another star (ZTF J0923+4236) was shown to dim irregularly every couple of months. During fainter states, this star shows chaotic variability on time scales of minutes before brightening again.

The team examined the third white dwarf (WD 1145+017) in 2015 and showed that it behaved close to theoretical predictions. Surprisingly, this study showed that the transits are now totally gone.

“The system is, overall, very gently getting brighter, as the dust produced by catastrophic collisions around 2015 disperses”, said Professor Gaensicke.

“The unpredictable nature of these transits can drive astronomers crazy – one minute they are there, the next they are gone. And this points to the chaotic environment they are in.”

What will happen to our solar system?

Professor Gaensicke said: “The sad news is that the Earth will probably just be swallowed up by an expanding Sun, before it becomes a white dwarf.

“For the rest of the solar system, some of the asteroids located between Mars and Jupiter, and maybe some of the moons of Jupiter may get dislodged and travel close enough to the eventual white dwarf to undergo the shredding process we have investigated.”

An international team of astronomers has used the Lovell telescope at Jodrell Bank to illuminate radio signals coming from a magnetar.

Researchers from the UK, Germany, and Australia have used the Lovell telescope to make a significant breakthrough in understanding the unprecedented behaviour of a previously dormant magnetar, known as XTE J1810-197.

Magnetars are a type of neutron star and the strongest magnets in the Universe.

At around 8,000 light years away, XTE J1810-197 is the closest magnetar known to Earth.

The magnetar emits light, which is strongly polarised and rapidly changing.

This implies that that interactions at the surface of the star are more complex than what is suggested in previous theoretical explanations.

The results are published in two papers in Nature Astronomy.

Close observation of the magnetar

Detecting radio signals from magnetars is extremely rare. XTE J1810-197 is one of the only magnetars known to produce these emissions.

The magnetar was first observed to emit radio signals in 2003 before going silent for over a decade.

In 2018, the signals were detected by The University of Manchester’s 76m Lovell telescope at the Jodrell Bank Observatory.

Subsequently, university scientists, working alongside institutions such as the Max Planck Institute for Radio Astronomy in Germany, Australia’s CSIRO national science agency, and the University of Southampton, have been closely monitoring the magnetar.

Significant changes in radio signals

Close monitoring has revealed significant changes in the radio signals coming from the magnetar, particularly in the way the light was polarised. This has indicated the magnetar’s radio beam shifting its direction in relation to Earth.

The team think that this was caused by an effect called free precession. This is where the magnetar wobbles slightly due to asymmetries in its structure, similar to a spinning top.

The wobbling motion unexpectedly decreased rapidly over a few months until it eventually stopped altogether.

This challenges the notion suggested by numerous astronomers that repeating fast radio bursts might originate from magnetars undergoing precession.

Gregory Desvignes from the Max Planck Institute for Radio Astronomy in Bonn, Germany, and lead author of one of the two papers, said: “We expected to see some variations in the polarisation of this magnetar’s emission, as we knew this from other magnetars but we did not expect that these variations are so systematic, following exactly the behaviour that would be caused by the wobbling of the star.”

Results yet to be determined

However, the cause behind the alteration of circular polarisation, where the light appears to spiral as it traverses through space, remains uncertain.

Dr Marcus Lower, a postdoctoral fellow at CSIRO, who led the Australian research using Murriyang, CSIRO’s Parkes radio telescope, said: “Our results suggest there is a superheated plasma above the magnetar’s magnetic pole, which is acting like a polarising filter. How exactly the plasma is doing this is still to be determined.”

Researchers from the Institute of Cosmology and Gravitation have helped to detect a gravitational-wave signal that could solve a key cosmic mystery.

The discovery of the gravitational-wave signal is from a set of results announced recently by the LIGO-Virgo-KAGRA collaboration, which comprises more than 1,600 scientists from around the world.

The collaboration includes members of the ICG, which aims to detect gravitational waves and use them to explore the fundamentals of science.

Observation of the gravitational-wave signal

Shortly after the start of the fourth LIGO-Virgo-KAGRA observing run in May 2023, the US LIGO Livingston detector observed a gravitational-wave signal from the collision of what is most likely a neutron star with a compact object 2.5 to 4.5 times the mass of the Sun.

Neutron stars and black holes are compact objects. What makes this signal, GW230529, interesting is the mass of the heavier object.

The object falls within a mass-gap between the heaviest known neutron stars and the lightest black holes.

The gravitational-wave signal cannot reveal the nature of this object by itself.

Therefore, future detections of similar events are required to solve this mystery.

“This detection, the first of our exciting results from the fourth LIGO-Virgo-KAGRA observing run, reveals that there may be a higher rate of similar collisions between neutron stars and low mass black holes than we previously thought,” said Dr Jess McIver, Assistant Professor at the University of British Columbia and Deputy Spokesperson of the LIGO Scientific Collaboration.

Assessing the reality of the event

As the event was only seen by one gravitational-wave detector, assessing whether it is real becomes more difficult.

Dr Gareth Cabourn Davies, a Research Software Engineer in the ICG, said: “Corroborating events by seeing them in multiple detectors is one of our most powerful tools in separating signals from noise.

“By using appropriate models of the background noise, we can judge an event even when we don’t have another detector to back up what we have seen.”

Previous way to detect masses of black holes and neutron stars

Before gravitational waves were detected in 2015, the masses of stellar-mass black holes were found using X-ray observations. The masses of neutron stars were found using radio observations.

The measurement fell into two distinct ranges, with a gap between them from about two to five times the mass of the Sun.

Over the years, some measurements have encroached on the mass gap, which is highly debated amongst astrophysicists.

Information provided by the newly detected signal

Analysis of the gravitational-wave signal shows that it came from the merger of two compact objects. One object had a mass between 1.2 and 2.0 times that of our Sun, and the other was slightly more than twice as big.

Although the gravitational-wave signal does not provide enough information to determine with certainty whether these objects are neutron stars or black holes, the lighter object is likely a neutron star, and the heavier one is a black hole.

Scientists in the LIGO-Virgo-KAGRA Collaboration are confident that the heavier object is within the mass gap.

Gravitation-wave signals have provided almost 200 measurements of compact-object masses. Of these, only one other merger may have involved a mass-gap compact object. The signal GW190814 came from the merger of a black hole with a compact object exceeding the mass of the heaviest known neutron stars and possibly within the mass gap.

“While previous evidence for mass-gap objects has been reported both in gravitational and electromagnetic waves, this system is especially exciting because it’s the first gravitational-wave detection of a mass-gap object paired with a neutron star,” said Dr Sylvia Biscoveanu from Northwestern University.

“The observation of this system has important implications for both theories of binary evolution and electromagnetic counterparts to compact-object mergers.”

The fourth observing run

The fourth observing run is planned to last for 20 months, including a break to make several improvements.

By 16 January 2024, when the current break started, a total of 81 significant signal candidates had been identified.

GW230529 is the first of these to be published after a detailed investigation.

The fourth run will resume on 10 April 2024 and will continue until February 2025 with no further planned breaks in observing.

While the run continues, the team will analyse the data from the first half of the run and check the remaining 80 significant signal candidates that have been identified.

By the end of the fourth observing run, the total number of observed gravitational-wave signals should exceed 200.