From Sky & Telescope : “Astronomers Watch Black Hole Jet Launch”

From Sky & Telescope

November 29, 2021
Lyndie Chiou

Astronomers have watched a jet launch from a stellar-mass black hole inside the Milky Way.

When X-rays flared from an area of the sky previously thought to be empty in March 2018, they triggered an early alert system. Astronomers around the world stopped what they were doing to turn six telescopes, including one aboard the International Space Station, toward the flare.

In the resulting observations, which ranged from radio to X-rays, Alex Tetarenko (The Texas Tech University (US)) and her collaborators caught something never seen before: the creation and launching of jets from a black hole, named MAXI J1820+070, about 10,000 light-years away in our galaxy. With observations in hand, they calculated physical properties of the jet, such as its distance and motion relative to the black hole.

“Jet materials alter the chemistry of interstellar gas and affect galaxy and star formation,” Tetarenko explains. “They also provide laboratories to test fundamental physics, so understanding what causes them is so important.”

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In this artist’s impression, a black hole is pulling in material from a companion star through an accretion disc. Some of that plasma escapes through a jet. Credit: Gabriel Pérez Díaz (IAC-Institute of Astrophysics of the Canaries[Instituto de Astrofísica de Canarias](ES).)

Most of the black holes we’ve discovered inside our galaxy have been detectable because they have a stellar companion. As a black hole pulls matter from its companion, the matter spirals inward, losing energy and emitting X-rays, just before entering the maw.

Jets then erupt from the black hole’s poles, propelling particles with such concentrated force that they fly out at relativistic speeds to light-years away emitting radio waves that can be detected from Earth.

Astronomers have observed jets around black holes large and small — recently, for example, the Event Horizon Telescope captured sharp images of jets from the supermassive black hole Messier 87*. But questions remain as to jets’ origins. Namely, where does all the jet-launching power come from?

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The Event Horizon Telescope obtained an unprecedentedly sharp image of the jet shooting out from the supermassive black hole in M87. But supermassive black holes and their jets usually change on timescales longer than human lifetimes. Around stellar-mass black holes, astronomers can watch such changes on shorter timescales. Credit: Radboud University Nijmegen [Radboud Universiteit](NL); WFI/The European Southern Observatory [Observatoire européen austral][Europäische Südsternwarte](EU)(CL); The MPG Institute for Radio Astronomy [MPG Institut für Radioastronomie](DE) / ESO’s Atacama Pathfinder Experiment(CL) / A. Weiss et al.; The National Aeronautics and Space Agency(US)/ The Chandra X-ray Center (US) / The Harvard Smithsonian Center for Astrophysics (US) / R. Kraft et al.; The Event Horizon Telescope-EHT / M. Janssen et al.

WFI Wide Field Imager on the 2.2 meter MPG/ESO telescope at Cerro LaSilla (CL)

MPG Institute for Astronomy [Max-Planck-Institut für Astronomie](DE)European Southern Observatory(EU)2.2 meter telescope at Cerro La Silla, Chile, 600 km north of Santiago de Chile at an altitude of 2400 metres.

ESO operates the Atacama Pathfinder Experiment, APEX, for The MPG Institute for Radio Astronomy [MPG Institut für Radioastronomie](DE) at one of the highest observatory sites on Earth, at an elevation of 5100 metres, high on the Chajnantor plateau in Chile’s Atacama region.

EHT map.

There are two competing theories: The jets could be extracting energy and angular momentum from the magnetic fields that thread the spinning black hole’s event horizon, or magnetic fields anchored in the materials swirling into the black hole could provide the needed power.

In order to answer these questions, we need to watch a full cycle to see a jet launch and extinguish. Stellar-mass black holes offer this opportunity because they run through an entire cycle in a few months, instead of taking millions of years as supermassive black holes do.

Mapping the Jet

MAXI J1820 flared when it caught an extra gob of gas from its stellar companion, which is about half the mass of the Sun. The team measured the outburst across a broad spectrum of wavelengths from X-rays to radio waves. Using a timing analysis method, they were finally able to resolve the tiny details of MAXI’s jets.

“The technique . . . is analogous to how ships use sonar to map underwater objects,” explains Tetarenko, “Except here, we use the timing signals propagating from inflow to outflow as ‘black hole sonar’ to map the jet structures.”

Timing analysis revealed the base height of the jets, their angle, and speed. This is important since properties like the magnetic field strength depend highly on the geometry.

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Observations from NASA’s Chandra X-ray Observatory taken in 2018 and 2019 (shown in inset) allowed astronomers to detect the black hole’s jets. Credit: X-ray: NASA / CXC / The University of Paris-Sorbonne [Université de Paris-Sorbonne](FR) / M. Espinasse et al.; Optical / IR: The University of Hawai’i (US) Pan-STARRS telescope.

National Aeronautics and Space Administration Chandra X-ray telescope(US)

U Hawaii (US) Pan-STARRS1 (PS1) Panoramic Survey Telescope and Rapid Response System is a 1.8-meter diameter telescope situated at Haleakala Observatories near the summit of Haleakala, altitude 10,023 ft (3,055 m) on the Island of Maui, Hawaii, USA. It is equipped with the world’s largest digital camera, with almost 1.4 billion pixels.

Calculations showed that MAXI J1820’s jets launched a mere light-second (300,000 km) away from the black hole, about 1,000 times closer than Earth is to the Sun. So close to the black hole, the jets are extremely narrow, opening at just 0.45 degrees, the narrowest angle measured to date.

Based on these results, published in The Astrophysical Journal, Andrzej Zdziarski (The Polish Academy of Sciences [Polska Akademia Nauk](PL)), Tetarenko, and Marek Sikora (also at Polish Academy of Sciences) think the black hole might be responsible for powering the jet. The energy the jet carries is consistent with theoretical predictions from the black hole spin scenario, Tetarenko says.

Tetarenko expects that deeper investigations into the data, as well as observations of more black hole systems, will help confirm the result.

“By simultaneously studying how the emission of the black hole X-ray binary changes from one part of the electromagnetic spectrum to another, Alex and her collaborators succeed in accurately measuring something that has never been possible in the past to this precision,” notes Sara Motta (The University of Oxford (UK), who wasn’t involved in the study. “This is crucial to constrain the fundamental physics ruling the jet generation and launching mechanism.”

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Sky & Telescope, founded in 1941 by Charles A. Federer Jr. and Helen Spence Federer, has the largest, most experienced staff of any astronomy magazine in the world. Its editors are virtually all amateur or professional astronomers, and every one has built a telescope, written a book, done original research, developed a new product, or otherwise distinguished him or herself.

Sky & Telescope magazine, now in its eighth decade, came about because of some happy accidents. Its earliest known ancestor was a four-page bulletin called The Amateur Astronomer, which was begun in 1929 by the Amateur Astronomers Association in New York City. Then, in 1935, the American Museum of Natural History opened its Hayden Planetarium and began to issue a monthly bulletin that became a full-size magazine called The Sky within a year. Under the editorship of Hans Christian Adamson, The Sky featured large illustrations and articles from astronomers all over the globe. It immediately absorbed The Amateur Astronomer.

Despite initial success, by 1939 the planetarium found itself unable to continue financial support of The Sky. Charles A. Federer, who would become the dominant force behind Sky & Telescope, was then working as a lecturer at the planetarium. He was asked to take over publishing The Sky. Federer agreed and started an independent publishing corporation in New York.

“Our first issue came out in January 1940,” he noted. “We dropped from 32 to 24 pages, used cheaper quality paper…but editorially we further defined the departments and tried to squeeze as much information as possible between the covers.” Federer was The Sky’s editor, and his wife, Helen, served as managing editor. In that January 1940 issue, they stated their goal: “We shall try to make the magazine meet the needs of amateur astronomy, so that amateur astronomers will come to regard it as essential to their pursuit, and professionals to consider it a worthwhile medium in which to bring their work before the public.”