Event Horizon Telescope: Moving towards a close-up of a black hole and its jets

(Press-News.org) After taking the first images of black holes, the ground-breaking Event Horizon Telescope (EHT) is poised to reveal how black holes launch powerful jets into space. Now, a research team led by Anne-Kathrin Baczko from Chalmers University of Technology in Sweden has shown that the EHT will be able to make exciting images of a supermassive black hole and its jets in the galaxy NGC 1052. The measurements, made with interconnected radio telescopes, also confirm strong magnetic fields close to the black hole’s edge. 

The main research question for the project’s scientists was how do supermassive black holes launch galaxy-size streams of high-energy particles – known as jets – into space at almost light-speed? Now, scientists have taken an important step towards being able to answer this question, with intricate measurements of the centre of the galaxy NGC 1052, at a distance of 60 million light years from Earth. 

The scientists made coordinated measurements using several radio telescopes, providing new insights into the workings of a galaxy and its supermassive black hole. The results are reported in a paper published in the scientific journal Astronomy & Astrophysics on 17 December 2024. 

A promising yet challenging target  The work has been led by Anne-Kathrin Baczko, astronomer at Onsala Space Observatory, Chalmers University of Technology.  

“The centre of this galaxy, NGC 1052, is a promising target for imaging with the Event Horizon Telescope, but it’s faint, complex and more challenging than all other sources we’ve attempted so far”, says Anne-Kathrin Baczko. 

The galaxy has a supermassive black hole that is the source of two powerful jets which stretch thousands of light years outwards through space.  

“We want to investigate not just the black hole itself, but also the origins of the jets which stream out from the east and west sides of the black hole as seen from Earth”, says Eduardo Ros, team member and astronomer at the Max Planck Institute for Radio Astronomy in Bonn, Germany. 

The team made measurements using just five of the telescopes in the EHT’s global network – including ALMA (the Atacama Large Millimeter/submillimeter Array) in Chile, in a configuration that would allow the best possible estimate of its potential for future observations, and supplemented with measurements from other telescopes. 

“For such a faint and unknown target, we were not sure if we would get any data at all. But the strategy worked, thanks in particular to the sensitivity of ALMA and complementary data from many other telescopes,” says Anne-Kathrin Baczko. 

Measurements show successful imaging possible in the future   The scientists are now convinced that successful imaging will be possible in the future, thanks to two new key pieces of information: The black hole’s surroundings shine brightly at just the right frequency of radio waves to be sure that they can be measured by the EHT.  The size of the region where the jets are formed is similar in size to the ring of M 87* – easily big enough to be imaged with the EHT at full strength.  From their measurements, the scientists have also estimated the strength of the magnetic field close to the black hole’s event horizon. The field strength, 2.6 tesla, is about 400 times stronger than the Earth’s magnetic field. That’s consistent with previous estimates for this galaxy. 

“This is such a powerful magnetic field that we think it can probably stop material from falling into the black hole. That in turn can help to launch the galaxy’s two jets”, says Matthias Kadler. 

Even though the source is as challenging as this, the future looks bright as radio astronomers prepare for new generations of telescope networks, like the NRAO’s ngVLA (next generation Very Large Array) and the ngEHT (The next generation Event Horizon Telescope). 

“Our measurements give us a clearer idea of how the innermost centre of the galaxy shines at different wavelengths. Its spectrum is bright at wavelengths around one millimetre, where we can make the very sharpest images today. It’s even brighter at slightly longer wavelengths, which makes it a prime target for the next generation of radio telescopes”, says team member Matthias Kadler, astronomer at the University of Würzburg in Germany. 

More about the research  The research paper, The putative center in NGC 1052, by Anne-Kathrin Baczko (Chalmers University of Technolgy, Sweden) and 286 co-authors, is published in the journal Astronomy & Astrophysics. The research team also includes Chalmers scientists John Conway and Michael Lindqvist (both Onsala Space Observatory) and Chiara Ceccobello (now at AI Sweden).  

The measurements were made by five telescopes in the EHT network: ALMA (the Atacama Large Millimeter/submillimeter Array) in Chile, the IRAM 30-metre telescope in Spain; the James Clerk Maxwell Telescope (JCMT) and the Submillimeter Array (SMA) in Hawaii; and the South Pole Telescope (SPT) in Antarctica. These were supplemented with measurements from 14 other radio telescopes in the GMVA network (Global Millimetre VLBI Array), in Spain, Finland and Germany, including the 20-metre telescope at Onsala Space Observatory, Sweden, and the telescopes of the VLBA (Very Long Baseline Array) in the US. 

The EHT Collaboration involves more than 400 researchers from Africa, Asia, Europe, North and South America. The international collaboration aims to capture the most detailed black hole images ever obtained by creating a virtual Earth-sized telescope.  

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