Strange cosmic coincidence: gamma-ray heartbeat puzzles scientists
The microquasar is located in the Milky Way and consists of a giant star and a black hole. The cloud is located in the constellation Aquila.
Previously published theoretical models did not predict such a result, which challenges common interpretations.
The study is led by a scientist from the DESY Laboratory in Hamburg and a researcher from the Institute of Space Studies of Catalonia (IEEC) at the Institute of Space Sciences (ICE, CSIC). The results are published in the journal Nature Astronomy.
Scientists have detected a mysterious gamma-ray heartbeat coming from a cosmic gas cloud. The unremarkable cloud, which is located in the constellation Aquila, is beating with the rhythm of a nearby black hole, indicating a connection between the two objects. The study, led by the DESY scientist Jian Li and ICREA Professor Diego F. Torres, a researcher from the Institute of Space Studies of Catalonia (IEEC) at the Institute of Space Sciences (ICE, CSIC), appears today in the journal Nature Astronomy.
Researchers rigorously analysed more than ten years of data from NASA's Fermi Gamma-ray Space Telescope, looking at a so-called microquasar. Microquasars, the local siblings of extragalactic quasars, are binary systems comprising a compact object and a companion star. By collecting matter from their companions, microquasars launch powerful winds and jets, influencing the interstellar environment around them. The system observed in this study, catalogued as SS 433, is one of the most famous systems of its kind and even though it has been studied for decades it still surprises researchers. Located some 15,000 light years away, within the Milky Way, it consists of a giant star of about 30 times the mass of our Sun and a black hole of 10 to 20 solar masses. The two objects are orbiting each other while the black hole sucks matter from the giant star.
“The material from the star accumulates in a disc around the black hole before falling into it like water in the whirl above the drain of a bathtub”, explains Li, a DESY researcher. “However, a part of that matter does not fall down the drain but shoots out at high speed in two narrow jets in opposite directions above and below the rotating disc”. “The accretion disc does not lie exactly in the plane of the orbit of the two objects but it sways like a spinning top that has been set up slanted on a table”, says Li. “As a consequence, the two jets spiral into the surrounding space, rather than just forming a straight line.”
The sway of the black hole's jets makes a complete round in about 162 days. The high-speed particles and the ultra-strong magnetic fields in the jet produce X-rays and gamma rays, the latter being observed by the team. A meticulous analysis revealed one gamma-ray signal with the same period coming from an unremarkable gas cloud located relatively far from the microquasar's jets. The consistent periods indicate the gas cloud's emission is powered by the microquasar.
“The timing signal we found provides an unambiguous connection between the microquasar and the cloud, separated by about 100 light years. This is as amazing as is intriguing, opening questions regarding how the black hole powers the cloud's heartbeat thus far”, says Torres, IEEC researcher at ICE-CSIC. An explanation that the team explored is based on the impact of fast protons produced at the ends of the jets, or near the black hole, that are injected into the cloud and hit the gas particles, producing gamma rays. Protons could also be part of an outflow of fast particles from the edge of the accretion disc. Whenever this outflow strikes the gas cloud, it lights up in gamma rays, explaining its strange heartbeat. “Energetically, the outflow from the disc could be as powerful as that of the jets and is believed to sway in solidarity with the rest of the system,” explains Torres.
Further observations as well as theoretical work are required to explain the gamma-ray heartbeat of this unique system beyond this initial discovery. “SS 433 continues to amaze observers at all frequencies and theoreticians alike,” emphasises Li. “And it is certain to provide a test-bed for our ideas on cosmic-ray production and propagation near microquasars for years to come.”
The research team led by Torres and Li is composed of international scientists from Spain (IEEC-ICE-CSIC), Germany (DESY), China (Nanjing University and Purple Mountain observatory) and USA (NRL).
Instruments
The Fermi Gamma-ray Space Telescope was launched from the Kennedy Space Center on 11 June 2008. Fermi has two gamma-ray instruments: the Large Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). The LAT is a wide-field gamma-ray telescope. From the start of regular observations, LAT scans the sky, providing all-sky coverage every two orbits. The GBM is an all-sky monitor that detects transient events such as occultations and gamma-ray bursts.
Diego F. Torres and Jian Li are Fermi-LAT members.
Images
Main image: Artistic view of SS 433 and the cosmic gas cloud. The microquasar SS 433 and its sway jet with helical structures are shown in the middle of the figure. In the foreground, the glowing of a molecular cloud represents the gamma-ray source revealed in this study. The concentric circles represent the gamma-ray heartbeat found, in synchrony with the SS 433 sway period. Credit: Konrad Rappaport, Susane Landis (Scicomlab for DESY), under advice by Jian Li (DESY), Diego F. Torres (ICREA / ICE, IEEC / CSIC).
Links
More information
This research is presented in a paper entitled “Gamma-ray heartbeat powered by the microquasar SS 433”, by Jian Li, D. F. Torres, Ruo-Yu Liu, Matthew Kerr, Emma de Oña Wilhelmi & Yang Su, that is published in the journal Nature Astronomy, 2020, on 17 August 2020.
The Institute of Space Studies of Catalonia (IEEC — Institut d’Estudis Espacials de Catalunya) promotes and coordinates space research and technology development in Catalonia for the benefit of society. IEEC fosters collaborations both locally and worldwide and is an efficient agent of knowledge, innovation and technology transfer. As a result of over 20 years of high-quality research, done in collaboration with major international organisations, IEEC ranks among the best international research centers, focusing on areas such as: astrophysics, cosmology, planetary science, and Earth Observation. IEEC’s engineering division develops instrumentation for ground- and space-based projects, and has extensive experience in working with private or public organisations from the aerospace and other innovation sectors.
IEEC is a private non-profit foundation, governed by a Board of Trustees composed of Generalitat de Catalunya and four other institutions that each have a research unit, which together constitute the core of IEEC R&D activity: the University of Barcelona (UB) with the research unit ICCUB — Institute of Cosmos Sciences; the Autonomous University of Barcelona (UAB) with the research unit CERES — Center of Space Studies and Research; the Polytechnic University of Catalonia (UPC) with the research unit CTE — Research Group in Space Sciences and Technologies; the Spanish Research Council (CSIC) with the research unit ICE — Institute of Space Sciences. IEEC is integrated in the CERCA network (Centres de Recerca de Catalunya).
Contacts
IEEC Communication Office
Barcelona, Spain
Ana Montaner Pizà
E-mail: comunicacio@ieec.cat
Institute of Space Sciences (ICE, CSIC)
Barcelona, Spain
Diego Torres
E-mail: dtorres@ice.csic.es
Deutsches Elektronen-Synchrotron DESY
Hamburg, Germany
Jian Li
E-mail: jian.li@desy.de