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Astronomers watch the launch of the Black Hole jet – Sky & Telescope


When x-rays erupted from an area of ​​the sky thought to be empty in March 2018, they triggered an early warning system. Astronomers around the world have stopped what they were doing to spin six telescopes, including one aboard the International Space Station, toward the eruption.

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

“The materials in the jets change the chemistry of interstellar gas and affect the formation of galaxies and stars,” explains Tetarenko. “They also provide labs to test fundamental physics, so it’s so important to understand their causes.”

Black hole jets

In this artist’s impression, a black hole attracts matter from a companion star through an accretion disk. Part of this plasma escapes by a jet.
Gabriel Pérez Díaz (Instituto de Astrofísica de Canarias)

Most of the black holes we have discovered inside our galaxy have been detectable because they have a stellar companion. When a black hole shoots matter from its mate, the matter coils inward, losing energy and emitting x-rays, just before entering the mouth.

Jets then shoot out of the black hole’s poles, propelling particles with such concentrated force that they fly away at relativistic speeds 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 M87 * black hole. But questions remain as to the origin of the jets. Namely, where does all the launching power of the jets come from?

Jet M87
The Event Horizon telescope obtained an unprecedented sharpness image of the jet emerging from the supermassive black hole of M87. But supermassive black holes and their jets typically change on time scales longer than human lifetimes. Around stellar mass black holes, astronomers can observe such changes on shorter time scales.
Radboud University; ESO / WFI; MPIfR / ESO / APEX / A. Weiss et al. ; NASA / CXC / CfA / R. Kraft et al. ; EHT / M. Janssen et al.

There are two competing theories: the jets could extract the energy and angular momentum from the magnetic fields that thread the rotating black hole’s event horizon, or the magnetic fields embedded in the materials swirling in the black hole could provide the power. necessary.

In order to answer these questions, we have to watch a full cycle to see a jet take off and go out. Stellar mass black holes provide this opportunity because they go through an entire cycle in a matter of months, instead of taking millions of years like supermassive black holes do.

Map the jet

The MAXI J1820 caught fire when it caught an extra drop of gas from its stellar companion, which is roughly half the mass of the Sun. The team measured the explosion over a wide spectrum of wavelengths, from x-rays to radio waves. Using a temporal 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 exit as than “black hole sonar” to map the structures of the jets. “

Temporal analysis revealed the base height of the jets, their angle and speed. This is important because properties such as the strength of the magnetic field are highly dependent on geometry.

X-ray observations of the stellar mass black hole
Observations from NASA’s Chandra X-ray Observatory taken in 2018 and 2019 (shown inset) allowed astronomers to detect black hole jets.
X-rays: NASA / CXC / University of Paris / M. Espinasse et al. ; Optical / IR: PanSTARRS

Calculations showed that the MAXI J1820’s jets launched a single light second (300,000 km) 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 Astrophysics Journal, Andrzej Zdziarski (Polish Academy of Sciences), Tetarenko and Marek Sikora (also from Texas Tech) believe that the black hole could be responsible for powering the jet. The energy carried by the jet is consistent with theoretical predictions of the black hole spin scenario, Tetarenko says.

Tetarenko expects further investigation of the data, as well as observations of more black hole systems, to help confirm the result.

“By simultaneously studying how the emission of the black hole’s x-ray binary changes from one part of the electromagnetic spectrum to another, Alex and his collaborators succeed in accurately measuring something that has never been possible in the past with this clarification, ”notes Sara. Motta (University of Oxford, UK), who did not participate in the study. “This is crucial in constraining the fundamental physics governing the mechanism for generating and launching the jet.”


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