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More than a hundred years have passed since Einstein formalized his theory of General Relativity (GR), the geometric theory of gravitation that revolutionized our understanding of the Universe. And yet, astronomers are still subjecting it to rigorous tests, hoping to find deviations from this established theory. The reason is simple: any indication of physics beyond GR would open new windows onto the Universe and help resolve some of the deepest mysteries about the cosmos.

One of the most rigorous tests ever was recently conducted by an international team of astronomers led by Michael Kramer of the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn, Germany. Using seven radio telescopes from across the world, Kramer and his colleagues observed a unique pair of pulsars for 16 years. In the process, they observed effects predicted by GR for the first time, and with an accuracy of at least 99.99%!

In addition to researchers from the MPIfR, Kramer and his associates were joined by researchers from institutions in ten different countries – including the Jodrell Bank Centre for Astrophysics (UK), the ARC Centre of Excellence for Gravitational Wave Discovery (Australia), the Perimeter Institute for Theoretical Physics (Canada), the Observatoire de Paris (France), the Osservatorio Astronomico di Cagliari (Italy), the South African Radio Astronomy Observatory (SARAO), the Netherlands Institute for Radio Astronomy (ASTRON), and the Arecibo Observatory.

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Pulsars are fast-spinning neutron stars that emit narrow, sweeping beams of radio waves. A new study identifies the origin of those radio waves. NASA’s Goddard Space Flight Center

“Radio pulsars” are a special class of rapidly rotating, highly magnetized neutron stars. These super-dense objects emit powerful radio beams from their poles that (when combined with their rapid rotation) create a strobing effect that resembles a lighthouse. Astronomers are fascinated by pulsars because they provide a wealth of information on the physics governing ultra-compact objects, magnetic fields, the interstellar medium (ISM), planetary physics, and even cosmology.

In addition, the extreme gravitational forces involved allow astronomers to test predictions made by gravitational theories like GR and Modified Newtonian Dynamics (MOND) under some of the most extreme conditions imaginable. For the sake of their study, Kramer and his team examined PSR J0737-3039 A/B, the “Double Pulsar” system located 2,400 light-years from Earth in the constellation Puppis.

This system is the only radio pulsar binary ever observed and was discovered in 2003 by members of the research team. The two pulsars that make up this system have rapid rotations – 44 times a second (A), once every 2.8 seconds (B) – and orbit each other with a period of just 147 minutes. While they are about 30% more massive than the Sun, they measure only about 24 km (15 mi) in diameter. Hence, their extreme gravitational pull and intense magnetic fields.

In addition to these properties, the rapid orbital period of this system makes it a near-perfect laboratory for testing theories of gravitation. As Prof. Kramer said in a recent MPIfR press release:

“We studied a system of compact stars that is an unrivalled laboratory to test gravity theories in the presence of very strong gravitational fields. To our delight we were able to test a cornerstone of Einstein’s theory, the energy carried by gravitational waves, with a precision that is 25 times better than with the Nobel-Prize winning Hulse-Taylor pulsar, and 1000 times better than currently possible with gravitational wave detectors.”

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Europa Clipper Could Help Discover if Jupiter’s Moon is Habitable

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Since 1979, when the Voyager probes flew past Jupiter and its system of moons, scientists have speculated about the possibility of life within Europa. Based on planetary modeling, Europa is believed to be differentiated between a rocky and metallic core, an icy crust and mantle, and a warm water ocean up to 100 km (62 mi) in depth. Scientists theorize that this ocean is maintained by tidal flexing, where interaction with Jupiter’s powerful gravitational field leads to geological activity in Europa’s core and hydrothermal vents at the core-mantle boundary.

Investigating the potential habitability of Europa is the main purpose of NASA’s Europa Clipper mission, which will launch on October 10th, 2024, and arrive around Jupiter in April 2030. However, this presents a challenge for astrobiologists since the habitability of Europa is dependent on many interrelated parameters that require collaborative investigation. In a recent paper, a team of NASA-led researchers reviewed the objectives of the Europa Clipper mission and anticipated what it could reveal regarding the moon’s interior, composition, and geology.

The team consisted of researchers from the Johns Hopkins University Applied Physics Laboratory (JHUAPL), the Beyond Center at Arizona State University, the Woods Hole Oceanographic Institution (WHOI), Honeybee Robotics, the Southwest Research Institute (SwRI), the Planetary Science Institute (PSI), the Lunar and Planetary Laboratory (LPL), NASA’s Goddard Space Flight Center (GSFC) and Jet Propulsion Laboratory (JPL), and multiple universities. Their paper, “Investigating Europa’s Habitability with the Europa Clipper,” recently appeared in Space Science Reviews.

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Could shallow lakes be locked away in Europa’s crust? Europa Clipper will find out. Credit: NASA

What is “Habitability”?

When it comes to the search for life beyond Earth (aka. astrobiology), all of humanity’s efforts are currently focused on Mars. This will change in the coming years as missions destined for the outer Solar System conduct detailed studies of “Ocean Worlds” – icy bodies with interior oceans. This includes Europa, Ganymede, Titan, Enceladus, Triton, and possibly Pluto and Charon. The Europa Clipper will be the first of these missions to arrive – followed by the ESA’s JUpiter ICy moons Explorer (JUICE) in 2031. It will spend the next four years orbiting Jupiter and making close flybys of Europa, studying its surface and interior with its advanced suite of instruments. As the Europa Study Team summarized in their 2012 report:

“Jupiter’s moon Europa is one the most promising candidates for hosting life today among ocean worlds in the Solar System. In its investigation of Europa’s habitability, the Europa Clipper mission seeks to understand the provenance of water, essential chemical elements and compounds, and energy, and how they might combine to make this moon’s environments suitable to support life.”

As the NASA-led team indicated in their study, the purpose of the Europa Clipper mission is not to detect life itself but to assess Europa’s ability to support life as we know it. This will consist of confirming (or refuting) the existence of Europa’s interior ocean and determining if it possesses the necessary chemical and energy sources for life to thrive. However, one of the main challenges in investigating the moon’s habitability is the nature of the concept itself. Nevertheless, the relevant parameters include hospitable temperatures, pressure, pH, salinity, and the presence of a solvent (such as water).

Steven D. Vance, the Deputy Section Manager for the Planetary Interiors and Geophysics Group at NASA’s Jet Propulsion Laboratory (JPL), was also the paper’s lead author. As he explained to Universe Today via email:

“Habitability is the potential for supporting life, but not necessarily the presence of life. Some environments are more habitable than others. For example, a lush rainforest provides
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NASA’s Interstellar Mapping Probe Prepares for a 2025 Launch

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Engineers at NASA have completed an important milestone in developing the Interstellar Mapping and Acceleration Probe (IMAP) spacecraft. It’s now moving from development and design to the assembly, testing, and integration phase, targeting a launch in late Spring 2025. After launch, the spacecraft will fly to the Earth-Sun L1 Lagrange Point and analyze how the Sun’s solar wind interacts with charged particles originating from outside the Solar System.

IMAP will follow up on discoveries and insights from the two Voyager spacecraft and the Interstellar Boundary Explorer (IBEX) and will help investigate two of the most important overarching issues in heliophysics: the energization of charged particles from the Sun and the interaction of the solar wind at its boundary with interstellar space.

The mission will map the boundaries of the heliosphere — the electromagnetic bubble surrounding and protecting our solar system — and help researchers better understand the boundary of the heliosphere.  This region is where the constant flow of particles from our Sun, called the solar wind, collides with material from the rest of the galaxy. This collision limits the amount of harmful cosmic radiation entering the heliosphere.  

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An updated model (left) suggests the shape of the Sun’s bubble of influence, the heliosphere, may be a deflated croissant shape, rather than the long-tailed comet shape suggested by other research (right). The white lines represent the solar magnetic field, while the red lines represent the interstellar magnetic field. Image Credits Opher, et al

It will also help settle the debate on the actual shape of the heliosphere. A study in 2020, using data from several spacecraft, suggested that the Sun’s bubble of influence may be a deflated croissant shape, rather than the long-tailed comet shape that has previously been

The spacecraft will be positioned about 1.5 million km (1 million miles) from Earth and will collect and analyze particles that make it through to help chart and understand the range of particles in interplanetary space.  

The milestone the IMAP mission recently met is called Key Decision Point D, which allows the mission to move from development and design to the testing and integration phase. The targeted launch date was moved back one months, from late April to May 2025 to ensure that the project team has the adequate resources to “address risks and technical complexities during system integration and testing,” NASA said in a recent mission blog post.

The spacecraft is currently being assembled inside the clean room at the Johns Hopkins Applied Physics Lab in Laurel, Maryland. There is a live, 24-hour feed where you can watch the assembly, integration, and testing.

During the next few months, engineers will install the electronics, communications systems, thermal systems, propulsion, batteries, and many more complex systems to make the spacecraft work. Additionally, all 10 of IMAP’s instruments will soon start to arrive from around the world and be integrated with the spacecraft one by one. Finally, the spacecraft will begin testing before being sent to NASA’s Goddard Space Flight Center for final testing prior to launch.

Learn more about the mission and the huge team of universities and organizations that are part of IMAP at the mission website.

The post NASA’s Interstellar Mapping Probe Prepares for a 2025 Launch appeared first on Universe Today.

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Does Betelgeuse Even Rotate? Maybe Not

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Betelgeuse is the well known red giant star in the corner of Orion the hunter. The name translated in some languages means ‘armpit of the giant’ which I think of all the star names, is simply the best! Betelgeuse has been fascinating observers of late not only because it unexpectedly faded a few years ago but more recently a study shows it’s super fast rotational speed which is, when compared to other supergiants, is like nothing seen before. 

One of the brightest stars in the northern hemisphere sky, in fact the tenth brightest, Betelgeuse has a stunning red colour. It is a semi regular variable star which means there is some regularity to its varied light output but there are occasions, perhaps lasting between 20 and 2000 days where the variation is interrupted. If Betelgeuse were placed in the Sun’s position then its visible surface would more than likely extend beyond the orbit of Mars and swallow up everything in between. 

Image showing the variability of Betelgeuse
1998/9 UV HST images of Betelgeuse showing asymmetrical pulsations with corresponding spectral line profiles (Credit :  STScI, NASA, ESA)

Like all stars, Betelgeuse rotates but a recent study using the Atacama Large Milimeter Array (ALMA) has showed that Betelgeuse is rotating faster than expected. Cool stars like Betelgeuse expand as they evolve and to conserve momentum the rotation must slow.  It is possible that mass loss due to stellar winds decreases rotation speeds further. The current theory predicts that red giants rotate at around 1km per second while red supergiants a little less than 0.1km per second. 

Image showing two of the receivers of the ALMA array in the Atacama Desert.
Two of the Atacama Large Millimeter/submillimeter Array (ALMA) 12-metre antennas (Credit : Iztok Bon?ina/ESO)

Current theory aside it seems there have been a number of observations of at least a few hundred giant stars rotating faster. Betelgeuse in particular has shown faster than expected rotation. Somewhat usefully, it’s proximity to Earth has meant its surface can be resolved and accurate measurements taken. Measurements showed that half of the visible hemisphere was blue shifted and the the other half red shifted. We can use this information to accurately calculate a rotational velocity.

When it comes to Betelgeuse, the radial velocity with ALMA was measured to be around 5.47 km per second. This value was compared against previous observations using Hubble Space Telescope and thankfully this agreed. One leading theory takes binary star evolution as a possible cause and in particular a merger with a low mass companion star. This is not an unusual process with an expected one-third of red supergiants experience stellar merger before their core collapses marking the end of their life. When it comes to red giants the team considered the impact of merging with planetary systems on the rotational velocity.

There are complications however in attaining sufficient data but the team modelled 3D radiation hydrodynamic simulations of red supergiants with properties similar to Betelgeuse. Throwing a proverbial spanner in the works, the team suggest that it is possible that the observations could be wrong and false signals have been picked up from churning convective plasma at the surface rather than the rotation of the star itself!

In an attempt to ascertain if it is possible to accurately measure the rotational speed of red giants and supergiants they had to develop new processing techniques to establish predictions that they could compare with observations of Betelgeuse. The team finally conclude that to be able to establish without doubt that Betelgeuse and other red supergiants are rotating
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