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Gravitational-wave astronomy is set to revolutionize our understanding of the cosmos. In only a few years it has significantly enhanced our understanding of black holes, but it is still a scientific field in its youth. That means there are still serious limitations to what can be observed.

Currently, all gravitational observatories are based on Earth. This makes the detectors easier to build and maintain, but it also means the observatories are plagued by background noise. Observatories such as LIGO and Virgo work by measuring the distance shift between mirrors as a gravitational wave passes through the observatory. This shift is extremely small. For mirrors placed 4 kilometers apart, the shift is a mere fraction of the width of a proton. The vibrations of a truck driving down a nearby road will shift the mirrors much more than that. So LIGO and Virgo use statistics and models of black hole mergers to distinguish a true signal from a false one.

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Theoretical observation range for GLOC. Credit: Jani, et al

Because of terrestrial background noise, current observatories focus on the high-frequency gravitational waves (10 – 1000 Hz) generated by black hole mergers. There has been discussion of building a space-based gravitational-wave observatory, such as LISA, which would observe low-frequency gravitational waves, such as those generated by early cosmic inflation. But many gravitational waves are in the intermediate range. To detect these, a recent study proposes building a gravitational-wave observatory on the Moon.

The Moon has long been a coveted location for astronomers. Optical telescopes on the Moon wouldn’t suffer from atmospheric blurring, and unlike space-based telescopes such as Hubble and Webb, they wouldn’t be limited by the size of your launch rocket. Most of the ideas proposed have been very hypothetical, but as we look towards a human return to the Moon in the next decade they are becoming less so. Already NASA is studying the construction of a radio telescope on the far lunar surface. Building a lunar gravitational-wave observatory would be significantly more challenging, but not impossible.

This recent study proposes a Gravitational-wave Lunar Observatory for Cosmology (GLOC). Rather than worrying about how such an observatory would be constructed, the study instead focuses on the sensitivity and observational limits of such an observatory. As you might expect, a lunar observatory wouldn’t suffer from the background vibrations that trouble Earth observatories. As a result, it could have a baseline four times longer than LIGO. This would give it a range on gravitational wave frequencies as low as a tenth of a Hertz. This would allow it to observe everything from stellar-mass binary mergers to those of intermediate-mass black holes.

But it would also be able to observe the same type of mergers as LIGO and Virgo at much greater distances. Distances so far that the gravitational waves have become very red-shifted. If constructed, GLOC would be able to use distant merger events to measure the rate of cosmic expansion across billions of years. This would be perhaps its greatest power because it would allow us to measure the Hubble parameter across much of cosmic history. We would finally learn whether cosmic expansion is part of the structure of spacetime, or whether it varies in time and space.

Of course, the GLOC proposal is purely hypothetical at this point. It will be at least decades before we would be able to build such an observatory. But this study shows that building such a telescope would be worth the effort.

Reference: Jani, Karan, and Abraham Loeb. “Gravitational-wave lunar observatory for cosmology.” Journal of Cosmology and Astroparticle Physics 2021.06 (2021): 044.

The post A Gravitational Wave Observatory on the Moon Could “Hear” 70% of the Observable Universe appeared first on Universe Today.

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Astronomers are Searching for a Galaxy-Wide Transmitter Beacon at the Center of the Milky Way

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June 4, 2023

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It has been over sixty years since the first Search for Extraterrestrial Intelligence (SETI) survey occurred. This was Project Ozma, a survey led by Dr. Frank Drake (who devised the Drake Equation) that used the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virginia, to listen for radio transmissions from Epsilon Eridani and Tau Ceti. While the search revealed nothing of interest, it paved the way for decades of research, theory, and attempts to find evidence of technological activity (aka. “technosignatures”).

The search continues today, with researchers using next-generation instruments and analytical methods to find the “needle in the cosmic haystack.” This is the purpose behind Breakthrough Listen Investigation for Periodic Spectral Signals (BLIPSS), a collaborative SETI project led by Cornell graduate student Akshay Suresh to look for technosignatures at the center of the Milky Way. In a recent paper, Suresh and his team shared their initial findings, which were made possible thanks to data obtained by the Greenbank Observatory and a proprietary algorithm they developed.

Suresh is a Ph.D. candidate at the Cornell Center for Astrophysics and Planetary Science who leads the BLIPPS campaign, a collaboration between Cornell University, the SETI Institute, and Breakthrough Listen. He and his colleagues were joined by astrophysicists from the Cahill Center for Astronomy and Astrophysics, the Institute for Mathematics, Astrophysics, and Particle Physics (IMAPP), the Institute of Space Sciences and Astronomy, and the International Centre for Radio Astronomy Research (ICRAR). Their paper, “A 4–8 GHz Galactic Center Search for Periodic Technosignatures,” appeared on May 30th in The Astronomical Journal.

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The Karl Jansky Very Large Array at night, with the Milky Way visible in the sky. Credit: NRAO/AUI/NSF; J. Hellerman

To date, all SETI surveys have been dedicated to looking for evidence of artificial radio transmissions. The accepted theory is that radio signatures would fall into one of two categories: narrowband intentional beacon emissions and broadband radiation leakage from radio transmitters. Of the two, the spectrotemporal characteristics (frequency over time) of radiation leakage are much harder to speculate about and likely to be weaker. For this reason, most modern SETI efforts have focused on looking for wideband searches for narrowband beacons from planetary systems or neighboring galaxies.

In particular, a rotating beacon near Galactic Center (GC) is considered a promising technosignature to SETI researchers. For an advanced species, such a beacon would provide a means for communicating with the entire galaxy without the need for direct contact. For species dying to know if they are alone in the Universe but not so eager as to advertise their location, a beacon is doubly attractive because it would also allow some anonymity to be maintained. As Suresh told Universe Today via email:

“From a game theory perspective, the core of the Milky Way is a likely “Schelling point” by which different alien worlds may establish communication without prior contact. For instance, intelligent aliens may choose to transmit beacons toward the center of the Milky Way to reach a maximum number of targets. Equivalently, such aliens may also transmit directly away from the center of the Milky Way, knowing that societies like ours will look towards the core of the galaxy.”

For their search, the team employed a fast folding algorithm (FFA), an open-source machine learning software designed to detect periodic events within time series data. They first tested this algorithm on known pulsars, successfully detecting the expected periodic emissions. They then consulted datasets obtained by the 100-meter Green Bank Telescope (GBT) – part of the Breakthrough Listen’s network – on a region at the center of the Milky Way during a 4.5-hour observing period. This region measures 50 light-years in diameter and encompasses over half a million stars.

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Jupiter’s “Stripes” Change Color. Now We Might Know Why

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June 4, 2023

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While Jupiter’s Great Red Spot is one of the most well-known spectacles in the solar system, Jupiter’s clouds and stripes that are responsible for the planet’s weather patterns are highly regarded, as well. Though not nearly as visible in an amateur astronomy telescope, Jupiter’s multicolored, rotating, and swirling cloud stripes are a sight to behold for any astronomy fan when seen in up-close images. And, what makes these stripes unique is they have been observed to change color from time to time, but the question of what causes this color change to occur has remained elusive.

This is what a recent study published in Nature Astronomy hopes to address as an international team of researchers examine how Jupiter’s massive magnetic field could be responsible for Jupiter’s changing stripe colors. This study was led by Dr. Kumiko Hori of Kobe University and Dr. Chris Jones of the University of Leeds and holds the potential to help scientists better understand how a planet’s magnetic field could influence a planet’s weather patterns. In this case, Jupiter’s massive magnetic field influencing its massive, swirling clouds.

“If you look at Jupiter through a telescope, you see the stripes, which go round the equator along lines of latitude,” explains Dr. Jones. “There are dark and light belts that occur, and if you look a little bit more closely, you can see clouds zipping around carried by extraordinarily strong easterly and westerly winds. Near the equator, the wind blows eastward but as you change latitude a bit, either north or south, it goes westward. And then if you move a little bit further away it goes eastward again. This alternating pattern of eastward and westward winds is quite different from weather on Earth.”

While previous studies have demonstrated that Jupiter’s appearance is somehow altered by infrared fluctuations approximately 50 km (31 mi) below the gas cloud surface, this most recent study demonstrates the infrared fluctuations could be caused by Jupiter’s magnetic field, the source of which, like Earth, is far deeper inside the planet.

“Every four or five years, things change,” said Dr. Jones. “The colors of the belts can change and sometimes you see global upheavals when the whole weather pattern goes slightly crazy for a bit, and it has been a mystery as to why that happens.”

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Infrared images of Jupiter obtained by a ground-based telescope displaying changes in the color of Jupiter’s clouds between 2001 and 2011 (dashed blue lines). (Credit: Arrate Antuñano/NASA/IRTF/NSFCam/SpeX)

For the study, the researchers analyzed data collected over several years from NASA’s Juno spacecraft to both observe and measure variations in Jupiter’s magnetic field, more commonly known as oscillations. Despite Jupiter’s massive radiation belt which can cause immense harm to any spacecraft, Juno has been orbiting the solar system’s largest planet since 2016 and is frequently lauded for it still being active despite the constant bombardment from the radiation.

From the data, the team was able to monitor the magnetic field’s waves and oscillations. They focused on a specific area of the magnetic field dubbed the Great Blue Spot, which is invisible to the naked eye and located near Jupiter’s equator. While this spot has been observed to be traveling eastwards on Jupiter, the data from this study indicates the spot is slowing down, which the team interprets as the start of an oscillation within the magnetic field, meaning the spot could eventually slow enough to where it reverses direction and starts traveling westwards.

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Still image taken from a video animation featuring Jupiter’s massive magnetic field at one instant in time, specifically its Great Blue Spot located near
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CRS-28 Mission

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June 3, 2023

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SpaceX is targeting Saturday, June 3 for Falcon 9’s launch of Dragon’s 28th Commercial Resupply Services (CRS-28) mission to the International Space Station from Launch Complex 39A (LC-39A) at NASA’s Kennedy Space Center in Florida. The instantaneous launch window is at 12:35 p.m. ET (16:35 UTC) and a backup launch opportunity is available on Sunday, June 4 at 12:12 p.m. ET (16:12 UTC).

This is the fifth flight of the first stage booster supporting this mission, which previously launched Crew-5, GPS III Space Vehicle 06, Inmarsat I-6 F2, and one Starlink mission. Following stage separation, Falcon 9 will land on the A Shortfall of Gravitas droneship in the Atlantic Ocean.

CRS-28 is the fourth flight for this Dragon spacecraft, which previously flew CRS-21, CRS-23, and CRS-25 to the space station. After an approximate 41-hour flight, Dragon will autonomously dock with the orbiting laboratory on Monday, June 5 at approximately 5:38 a.m. ET (9:38 UTC).

A live webcast of this mission will begin about 20 minutes prior to liftoff.

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