Gravity and dark matter, a bond beyond distances
A SISSA study proposes a new model of non-local interaction between the dark matter of a galaxy and gravity
Peer-Reviewed PublicationIMAGE: DWARF GALAXY view more
CREDIT: NASA'S GODDARD SPACE FLIGHT CENTER/JENNY HOTTLE
Isaac Newton formulated his theory of gravity as an action at a distance: a planet instantly feels the influence of another celestial body, no matter the distance between them. This characteristic motivated Einstein to develop the famous theory of general relativity, where gravity becomes a local deformation of spacetime. The principle of locality states that an object is directly influenced only by its surrounding environment: distant objects cannot communicate instantaneously, only what is here right now matters. However, in the past century, with the birth and development of quantum mechanics, physicists discovered that non-local phenomena not only exist but are fundamental to understanding the nature of reality. Now, a new study from SISSA – Scuola Internazionale Superiore di Studi Avanzati, recently published in The Astrophysical Journal, suggests that dark matter, one of the most mysterious components of the Universe, interacts with gravity in a non-local way. According to the authors, PhD students Francesco Benetti and Giovanni Gandolfi, along with their supervisor Andrea Lapi, this discovery could provide a fresh perspective on the still unclear nature of dark matter.
Dark matter is a fundamental component of nature: it is responsible for the formation of the structures we observe in the Universe today and surrounds luminous matter in galaxies, contributing to the motion of the stars we see in the sky. However, the nature of dark matter, especially its interaction with gravity in smaller galaxies, remains mysterious. "In recent decades, the scientific community has made great efforts to understand these enigmatic phenomena, but many questions remain unanswered. To explore the nature of dark matter and its interaction with gravity, a new approach may be necessary," explain the authors of the study. The new research from SISSA has precisely explored this intriguing path.
The study proposes a new model of non-local interaction between the dark matter of a galaxy and gravity: "It's as if all the matter in the universe tells the dark matter in a galaxy how to move," state the authors. To model this non-locality, fractional calculus has been employed, a mathematical tool first developed in the 17th century and recently found applications in various areas of physics. The power of this calculus had never been tested in astrophysics before. "We wondered if fractional calculus could be the key to understanding the mysterious nature of dark matter and its interaction with gravity, and surprisingly, experimental results on thousands of galaxies of different types have shown that the new model more accurately describes the motion of stars compared to the standard theory of gravity," explain the authors. This non-locality appears to emerge as a collective behavior of dark matter’s particles within a confined system, proving particularly relevant in small-sized galaxies. A thorough understanding of this phenomenon could bring us closer what dark matter really is.
"However, many questions remain to be answered," emphasize the authors. "How does non-locality precisely emerge? What are its implications within larger structures, such as galaxy clusters, or in the phenomenon of gravitational lensing, which allows us to observe distant celestial objects?" Moreover, it will be necessary to reconsider the standard model of cosmology considering this new mechanism. "Further studies will be conducted to explore all these implications and more. We wouldn't be surprised to discover that other unresolved questions about the Universe could be resolved by the newly proposed non-locality." Advancements in understanding the nature of dark matter represent a significant step towards a better knowledge of our Universe. Ongoing research continues to provide new perspectives and brings us closer to a comprehensive understanding of the phenomena that surround us.
JOURNAL
The Astrophysical Journal
METHOD OF RESEARCH
Data/statistical analysis
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Dark Matter in Fractional Gravity. I. Astrophysical Tests on Galactic Scales
FAST finds missing link in evolution of
spider pulsar system
IMAGE: PICTURE OF M71E (THE PULSAR BINARY ON THE RIGHT OF THE FIGURE), FAST (BOTTOM OF THE FIGURE) AND THE GLOBULAR CLUSTER M71 (BACKGROUND) view more
CREDIT: SCIENCEAPE/CAS/NAOC
Researchers from the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) and their collaborators at home and abroad have discovered a binary pulsar with a 53-minute orbital period using the Five-hundred-meter Spherical radio Telescope (FAST). The discovery of this binary system—named PSR J1953+1844 or M71E—fills the gap in the evolution of spider pulsar systems.
The findings were published in Nature on June 20.
The first pulsar was discovered in 1967. As of now, about 3,000 of these fascinating objects, which rotate regularly and quickly like spinning tops in the sky, have been found.
Some pulsars are located in binary systems, orbiting with companion stars. If the two stars are close together, the pulsar will swallow material from the companion star to keep spinning. At the beginning, the companion star is heavy. But as the pulsar "eats" its companion star, the two stars get closer together and orbit each other with increasing speed. In contrast, as the star loses mass and gets lighter, the pulsar can't continue to plunder and thus pushes the companion star away. As a result, the pulsar's orbital speed slows down.
This behavior, which is reminiscent of female spiders eating male spiders, inspired astronomers to name the objects in these two stages after redback and black widow spiders, respectively. They are collectively known as spider pulsars.
The evolution from redback to black widow takes a long time, up to hundreds of millions of years. Previously, only binary pulsar systems in the redback and black widow states had been detected, with no intermediate states yet found. The reason is that the orbital period of the intermediate pulsar predicted by this theory would be very short and the distance between the two stars would be very close, thus posing challenges for observation. For this reason, the theory of the evolution of spider pulsar systems from redback to black widow had not been fully proved.
Now, however, the possibility of this evolutionary path has been confirmed by FAST, the world's largest and most sensitive radio telescope. The research team used long-term observation by FAST to detect a spider pulsar system whose orbital duration is the shortest ever discovered—only 53 minutes. Based on various indications during observation, the researchers determined that the system was in an intermediate state on the evolutionary path from redback to black widow, thus filling in the missing link in spider pulsar evolution theory.
"The orbital of the binary is almost face-on—such a system is extremely rare. FAST found it in the vast sea of stars using its extremely high detection capabilities. This filled the gap in the evolution of spider pulsar systems and reflects [FAST's] unprecedented sensitivity," said JIANG Peng of NAOC, co-corresponding author of the study.
Nature reviewers described the result as a "very interesting pulsar binary system. This discovery shortens the record for the shortest orbital period of a pulsar binary system by about 30%, indicating a new and unknown process in the evolution of spider pulsars."
This work was conducted in collaboration with Guizhou University, the Yunnan Astronomical Observatory, the Shanghai Astronomical Observatory, the National Time Service Center, Peking University, the University of the Chinese Academy of Sciences, the Max Planck Institute in Germany, and the University of Nevada, Las Vegas.
JOURNAL
Nature
ARTICLE TITLE
A Binary Pulsar in a 53-minute Orbit
'Smiling cat' nebula captured in new ESO image
IMAGE: THIS SPECTACULAR PICTURE OF THE SH2-284 NEBULA HAS BEEN CAPTURED IN GREAT DETAIL BY THE VLT SURVEY TELESCOPE AT ESO’S PARANAL OBSERVATORY. SH2-284 IS A STAR FORMATION REGION, AND AT ITS CENTRE THERE IS A CLUSTER OF YOUNG STARS, DUBBED DOLIDZE 25. THE RADIATION FROM THIS CLUSTER IS POWERFUL ENOUGH TO IONISE THE HYDROGEN GAS IN THE NEBULA’S CLOUD. IT IS THIS IONISATION THAT PRODUCES ITS BRIGHT ORANGE AND RED COLOURS. THIS IMAGE IS PART OF THE VST PHOTOMETRIC HΑ SURVEY OF THE SOUTHERN GALACTIC PLANE AND BULGE (HTTPS://WWW.VPHASPLUS.ORG/), LED BY JANET DREW AT THE UNIVERSITY OF HERTFORDSHIRE IN THE UK. view more
CREDIT: ESO/VPHAS+ TEAM. ACKNOWLEDGEMENT: CASU
This cloud of orange and red, part of the Sh2-284 nebula, is shown here in spectacular detail using data from the VLT Survey Telescope, hosted by the European Southern Observatory (ESO). This nebula is teeming with young stars, as gas and dust within it clumps together to form new suns. If you take a look at the cloud as a whole, you might be able to make out the face of a cat, smiling down from the sky.
The Sh2-284 stellar nursery is a vast region of dust and gas and its brightest part, visible in this image, is about 150 light-years (over 1400 trillion kilometers) across. It’s located some 15 000 light-years away from Earth in the constellation Monoceros.
Nestled in the centre of the brightest part of the nebula — right under the ‘cat’s nose’ — is a cluster of young stars known as Dolidze 25, which produces large amounts of strong radiation and winds. The radiation is powerful enough to ionise the hydrogen gas in the cloud, thereby producing its bright orange and red colours. It’s in clouds like this that the building blocks for new stars reside.
The winds from the central cluster of stars push away the gas and dust in the nebula, hollowing out its centre. As the winds encounter denser pockets of material, these offer more resistance meaning that the areas around them are eroded away first. This creates several pillars that can be seen along the edges of Sh2-284 pointing at the centre of the nebula, such as the one on the right-hand side of the frame. While these pillars might look small in the image, they are in fact several light-years wide and contain vast amounts of gas and dust out of which new stars form.
This image was created using data from the VLT Survey Telescope (VST), which is owned by The National Institute for Astrophysics in Italy, INAF, and is hosted at ESO’s Paranal Observatory in Chile. The VST is dedicated to mapping the southern sky in visible light and makes use of a 256-million-pixel camera specially designed for taking very wide-field images. This image is part of the VST Photometric Hα Survey of the Southern Galactic Plane and Bulge (VPHAS+), which has studied some 500 million objects in our home galaxy, helping us better understand the birth, life, and eventual death of stars within our Milky Way.
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A surprise chemical find by ALMA may help detect and confirm protoplanets
IMAGE: LOCATED IN THE CONSTELLATION SAGITTARIUS, THE YOUNG STAR HD 169142 IS HOST TO A GIANT PROTOPLANET EMBEDDED WITHIN ITS DUSTY, GAS-RICH PROTOPLANETARY DISK. THIS ARTIST’S CONCEPTION SHOWS THE JUPITER-LIKE PLANET INTERACTING WITH AND HEATING NEARBY MOLECULAR GAS, DRIVING OUTFLOWS SEEN IN SEVERAL EMISSION LINES, INCLUDING THOSE FROM SHOCK-TRACING MOLECULES LIKE SO AND SIS, AND THE COMMONLY SEEN 12CO AND 13CO. view more
CREDIT: CREDIT: ALMA (ESO/NAOJ/NRAO), M. WEISS (NRAO/AUI/NSF)
Scientists using the Atacama Large Millimeter/submillimeter Array (ALMA) to study the protoplanetary disk around a young star have discovered the most compelling chemical evidence to date of the formation of protoplanets. The discovery will provide astronomers with an alternate method for detecting and characterizing protoplanets when direct observations or imaging are not possible. The results will be published in an upcoming edition of The Astrophysical Journal Letters.
HD 169142 is a young star located in the constellation Sagittarius that is of significant interest to astronomers due to the presence of its large, dust- and gas-rich circumstellar disk that is viewed nearly face-on. Several protoplanet candidates have been identified over the last decade, and earlier this year, scientists at the University of Liège and Monash University confirmed that one such candidate— HD 169142 b— is, in fact, a giant Jupiter-like protoplanet. The discoveries revealed in a new analysis of archival data from ALMA— an international collaboration in which the National Science Foundation’s National Radio Astronomy Observatory (NRAO) is a member— may now make it easier for scientists to detect, confirm, and ultimately characterize, protoplanets forming around young stars.
“When we looked at HD 169142 and its disk at submillimeter wavelengths, we identified several compelling chemical signatures of this recently-confirmed gas giant protoplanet,” said Charles Law, an astronomer at the Center for Astrophysics | Harvard & Smithsonian, and the lead author of the new study. “We now have confirmation that we can use chemical signatures to figure out what kinds of planets there might be forming in the disks around young stars.”
The team focused on the HD 169142 system because they believed that the presence of the HD 169142 b giant protoplanet was likely to be accompanied by detectable chemical signatures, and they were right. Law’s team detected carbon monoxide (both 12CO and its isotopologue 13CO) and sulfur monoxide (SO), which had previously been detected and were thought to be associated with protoplanets in other disks. But for the first time, the team also detected silicon monosulfide (SiS). This came as a surprise because in order for SiS emission to be detectable by ALMA, silicates must be released from nearby dust grains in massive shock waves caused by gas traveling at high velocities, a behavior typically resulting from outflows that are driven by giant protoplanets. “SiS was a molecule that we had never seen before in a protoplanetary disk, let alone in the vicinity of a giant protoplanet,” Law said. “The detection of SiS emission popped out at us because it means that this protoplanet must be producing powerful shock waves in the surrounding gas.”
With this new chemical approach for detecting young protoplanets, scientists may be opening a new window on the Universe and deepening their understanding of exoplanets. Protoplanets, especially those that are still embedded in their parental circumstellar disks such as in the HD 169142 system, provide a direct connection with the known exoplanet population. “There’s a huge diversity in exoplanets and by using chemical signatures observed with ALMA, this gives us a new way to understand how different protoplanets develop over time and ultimately connect their properties to that of exoplanetary systems,” said Law. “In addition to providing a new tool for planet-hunting with ALMA, this discovery opens up a lot of exciting chemistry that we’ve never seen before. As we continue to survey more disks around young stars, we will inevitably find other interesting but unanticipated molecules, just like SiS. Discoveries such as this imply that we are only just scratching the surface of the true chemical diversity associated with protoplanetary settings.”
The National Radio Astronomy Observatory (NRAO) is a major facility of the National Science Foundation (NSF) operated under a cooperative agreement by Associated Universities, Inc.
About ALMA
The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Organisation for Astronomical Research in the Southern Hemisphere (ESO), the U.S. National Science Foundation (NSF), and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science and Technology Council (NSTC) in Taiwan and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).
ALMA construction and operations are led by ESO on behalf of its Member States; by theNational Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning, and operation of ALMA.
Astronomers find a planet that shouldn't exist
When our sun reaches the end of its life, it will expand to 100 times its current size, enveloping the Earth. Many planets in other solar systems face a similar doom as their host stars grow old. But not all hope is lost, as astronomers from the University of Hawaiʻi Institute for Astronomy (UH IfA) have made the remarkable discovery of a planet's survival after what should have been certain demise at the hands of its sun.
The Jupiter-like planet 8 UMi b, officially named Halla, orbits the red giant star Baekdu (8 UMi) at only half the distance separating the Earth and the sun. Using two Maunakea Observatories on Hawaiʻi Island—W. M. Keck Observatory and Canada-France-Hawaiʻi Telescope (CFHT)—a team of astronomers led by Marc Hon, a NASA Hubble Fellow at UH IfA, has discovered that Halla persists despite the normally perilous evolution of Baekdu.
Using observations of Baekdu's stellar oscillations from NASA's Transiting Exoplanet Survey Satellite (TESS), they found that the star is burning helium in its core, signaling that it had already expanded enormously into a red giant star once before. The work is published in the journal Nature.
The star would have inflated up to 1.5 times the planet's orbital distance—engulfing the planet in the process—before shrinking to its current size at only one-tenth of that distance.
"Planetary engulfment has catastrophic consequences for either the planet or the star itself—or both. The fact that Halla has managed to persist in the immediate vicinity of a giant star that would have otherwise engulfed it highlights the planet as an extraordinary survivor," said Hon, the lead author of the study.
Maunakea observatories confirm the survivor
The planet Halla was discovered in 2015 by a team of astronomers from Korea using the radial velocity method, which measures the periodic movement of a star due to the gravitational tug of the orbiting planet. Following the discovery that the star must at one time have been larger than the planet's orbit, the IfA team conducted additional observations from 2021–2022 using Keck Observatory's High-Resolution Echelle Spectrometer (HIRES) and CFHT's ESPaDOnS instrument. These new data confirmed the planet's 93-day, nearly circular orbit had remained stable for over a decade and that the radial velocity changes must be due to a planet.
"Together, these observations confirmed the existence of the planet, leaving us with the compelling question of how the planet actually survived," said IfA astronomer Daniel Huber, second author of the study. "The observations from multiple telescopes on Maunakea was critical in this process."
Escaping engulfment
At a distance of 0.46 astronomical units (AU, or the Earth-sun distance) to its star, the planet Halla resembles "warm" or "hot" Jupiter-like planets that are thought to have started on larger orbits before migrating inward close to their stars. However, in the face of a rapidly evolving host star, such an origin becomes an extremely unlikely survival pathway for planet Halla.
Another theory for the planet's survival is that it never faced the danger of engulfment. Similar to the famous planet Tatooine from Star Wars, which orbits two suns, the team believes the host star Baekdu may have originally been two stars. A merger of these two stars may have prevented any one of them from expanding sufficiently large enough to engulf the planet.
A third possibility is that Halla is a relative newborn—that the violent collision between the two stars produced a gas cloud from which the planet formed. In other words, the planet Halla may be a recently-born "second generation" planet.
"Most stars are in binary systems, but we don't yet fully grasp how planets may form around them. Therefore, it's plausible that more planets may actually exist around highly evolved stars thanks to binary interactions," explained Hon.
More information: Marc Hon, A close-in giant planet escapes engulfment by its star, Nature (2023). DOI: 10.1038/s41586-023-06029-0. www.nature.com/articles/s41586-023-06029-0
Journal information: Nature
Provided by University of Hawaii at Manoa New era of exoplanet discovery begins with images of 'Jupiter's younger sibling'
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