The first detection of gravitational waves (GW) by researchers at the Laser Gravitational-Wave Observatory (LIGO) in 2015 revolutionized astronomy. This phenomenon consists of ripples in space-time caused by the merger of massive objects and was predicted a century ago by Einstein’s theory of general relativity. In the coming years, this burgeoning field will advance dramatically thanks to the introduction of next-generation observatories, such as the Laser Interferometer Space Antenna (LISA).
With greater sensitivity, astronomers will be able to trace GW events back to their source and use them to probe the interiors of UFOs and the laws of physics. As part of the Voyage 2050 planning cycle, the European Space Agency (ESA) is studying important topics that could be ready by 2050 – including GW astronomy. In a recent paper, researchers from the Division of Mission Analysis at the European Space Agency and the University of Glasgow present a new concept that would build on LISA – known as LISAmax. As they report, this observatory can improve the sensitivity of GW by twofold.
The research was led by theoretical physicist Dr Waldemar Martins, mission analyst at the European Space Agency’s European Space Operations Center (ESOC) in Darmstadt, Germany. He was joined by space engineer and astrophysicist Michael Khan, also a mission analyst at ESOC, and astrophysicist Dr Jean-Baptiste Pyle, a research fellow in astronomy and astrophysics at the University of Glasgow. The paper describing their findings has appeared online at arXiv Prepress server recently and is currently being reviewed for publication by the journal Classical and quantitative gravity.
Since LIGO scientists first detected them in 2015, researchers at LIGO and other observatories around the world have refined the types of GW events they can detect. These include the Virgo Observatory in Italy (near Pisa) and the Kamioka Gravitational Wave Detector (KAGRA) in Hida, Japan. Since then, these observatories have partnered with LIGO, forming the Ligo-Virgo-KAGRA (LVK) Collaboration. The efforts of these and other observatories, as well as upgrades that provided increased sensitivity, have doubled the number of detected events and even traced some back to their sources.
As Dr. Martens told Universe Today via email, this pioneering work has been invaluable. But like all forms of astronomy, future progress depends in part on having observatories in space:
“Now that there is no doubt that gravitational waves can be measured, astronomers want to use them as an additional source of information where previously only electromagnetic waves were available. Ground-based detectors, such as LIGO/Virgo/Kagra are sensitive in the frequency range tens of hertz to several kilohertz, This makes it sensitive to sources such as mergers of black holes of tens of solar masses.
“However, much larger objects, such as supermassive black holes (greater than 10^6 solar masses), are known to be found at the center of galaxies. The mergers of these objects produce gravitational waves far below the sensitive range of ground-based detectors. To see them, we have to go into space and create an observatory, like LISA, with an arm span of 2.5 million km.
So far, astronomers have detected GW events caused by binary black holes (BBHs) or binary neutron stars (kilonova events), where co-orbiting objects eventually merge. It is also assumed that there are many other possible sources, and studying these events can advance our understanding of the universe. “Among them are the primordial gravitational waves that were produced during operations a split second after the Big Bang,” said Dr. Martins. “We hope that LISA will be able to detect this, but it is not yet clear. This is one of the reasons why detectors with higher sensitivity and/or different frequency bands should be considered for the Voyage 2050 program.”
Voyager 2050 is the latest planning cycle to become part of the agency’s science programme, and the foundation and main “mandatory programme” of the European Space Agency. All member states must contribute, and scientific objectives, proposals, and funding are selected by unanimous decision. These courses aim to define a long-term funding horizon that will allow Member States to plan their priorities ahead of time and provide the European scientific community with a clear vision of research areas worthy of investment and development.
Since the 1980s, the program has been planned with cycles of about 20 years, corresponding to the amount of time needed to prepare ambitious space missions. The first planning cycle (Horizon 2000) was established in 1984 and consisted of decisions that led to the Solar and Heliospheric Observatory (SOHO) missions and the cluster, Rosetta, XMM-Newton, and Herschel from the mid-1990s to the early 2000s. In 2005, another planning cycle (the World Vision) was launched, including proposals for missions to be realized between 2015 and 2025.
This paved the way for missions such as the recently launched JUpiter ICy Satellite Explorer (JUICE), the Advanced Telescope for High Energy Astrophysics (ATHENA) and the X-ray Observatory LISA due to launch by 2030. The latest cycle, Voyage 2050, was initiated by ESA Science Director Carol Mundell to select science properties To follow up on the ATHENA and LISA missions. While these missions will be game-changers, particularly in collaboration, Dr. Martins and colleagues suggest ways in which the LISA mission could be further enhanced. As he explained:
“The basic idea of LISAmax is to detect GW at even lower frequencies than LISA can do. To be sensitive to these frequencies, one must increase the laser arms of the detector. Larger arms mean greater wavelengths and, therefore, lower frequencies.” Three LISAmax spacecraft were positioned “They are close to the trigonometric Lagrangian points in the Sun-Earth system, giving the detector an arm’s length of 259 million km. For comparison, LISA’s arms are 2.5 million km long. This makes LISAmax sensitive to GWs in the micro-Hertz band and opens a new window to GW astronomy.”
In general, any source that can be measured by LISA below 1 megahertz can be measured with LISAmax at about two orders of magnitude better signal-to-noise. An example discussed in the paper is the inspiratory phase of supermassive black hole binaries. Whereas, LISA will only be able to see such sources shortly before the final fusion event, LISAmax can observe these objects thousands of years in advance, allowing for a much better measurement of certain parameters.”
The scientific community is studying this concept, which could have drastic implications for the future of GW astronomy. In addition to expanding the range of detectable GW events, next-generation GW observatories can trace more events back to their sources. Moreover, astronomers anticipate that GWs will allow them to explore the laws of physics, investigate the interiors of extreme objects, and even help study planets and satellites.
The proposal by Dr. Martens and colleagues is one of several GW concepts submitted to ESA for the Voyage 2050 program. These concepts include a space interferometer that would scan the sky for GWs in millhertz to microhertz (MHz to µ-Hz) Frequency range. Another suggests how sensitive gigawatt interferometers in the megahertz range can be used to learn more about the nature of black holes. Others show how observations in the decihertz (dHz) range can provide the “missing link” to GW astronomy, while high-angle astronomy can help trace GWs to their source.
Research into the physics of the early universe, which includes the study of the primordial gravitational wavesis also a major topic of ESA’s Voyage 2050 program. By examining GWs created during the inflationary era, scientists will finally be able to explore the physics and microphysics of this early cosmic period.
Waldemar Martins et al., Lisamax: improving sensitivity to gravitational waves by two orders of magnitude, arXiv (2023). doi: 10.48550/arxiv.2304.08287
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