Science1 publisher3 min readPublished
Astronomers place a candidate microblazar inside the Milky Way, with one jet aimed at Earth
Josep Martí and Pedro Luque-Escamilla say IRAS 18293-0941, an object in a 1983 catalog, is a small black hole in our galaxy with a jet aimed at Earth. If it holds up, it ends a search for a nearby blazar that has run for nearly 35 years.
The Scientist · Science desk
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What happened
- Modern radio data on the catalog object showed a small, very bright source with extra light on only one side, the pattern Martí calls the fingerprint of blazars.
- The pair first took it for another distant blazar, but data from three observatories on the ground and in space placed it inside the Milky Way.
- The findings are due in a forthcoming paper in Astronomy & Astrophysics.
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Why it matters
- capability A jet that varies over days or weeks lets astronomers follow, in an ordinary observing campaign, behaviour that a supermassive blazar spreads over thousands of years.
- constraint Until observations connect the hidden jet to the particle patch, the accelerator idea is a hypothesis based on position in the sky, and the origin of those particles remains unexplained.
- precedent Tetarenko's comments set evidence from many telescopes and wavelengths as the standard against which the next microblazar claim will be judged.
Distance has been the obstacle all along. Luque-Escamilla, of the University of Jaén in Spain, and Martí have spent two decades searching archival telescope data for these objects, with little success [6]. "We found many candidates in the past," Martí said. "They turned out to be extragalactic objects" [7]. They picked IRAS 18293-0941 out of a 1983 catalog made by a Dutch-American spacecraft [8]. Its one-sided radio signature is the same one full-sized blazars show, and at first the pair assumed it was another distant one [9][10].
Placing it inside the galaxy took data from three observatories on the ground and in space [10]. Alexandra Tetarenko of the University of Lethbridge in Canada, who was not involved, said the range of evidence is what sets the claim apart. "The authors took a truly multi-wavelength approach, making use of all different types of astrophysical data from many telescopes," she said. "This is not only what distinguishes this work from past claims on other microblazar candidates but also makes it far more convincing" [11]. The Science News report does not name the three observatories or give the object's distance or black-hole mass. Those will have to come from the paper [2].
Small black holes are worth the trouble because they change quickly. A blazar is a quasar, a supermassive black hole feeding from a disk of material, with one of its jets pointed roughly at Earth [3]. In a microquasar, a small black hole feeds on a large star, and material falls in faster than it does around the giants [4]. "What takes days or weeks to change in a microblazar would take thousands of years in a supermassive blazar," Luque-Escamilla said. "It's a perfect scale model where we can watch a 'cosmic movie' in fast-forward" [5]. Compare one week with 1,000 years and the factor is about 52,000 [13].
The particle claim is a separate argument, and the weaker one as reported. Ultrahigh-energy particles arrive carrying 100 times the energy the Large Hadron Collider can create, and scientists have struggled to explain what accelerates them [12]. What ties them to IRAS 18293-0941 is that the object sits quite near a known patch of them [12]. Martí and his colleagues put the accelerator at the far end of the invisible jet pointing away from Earth, where it would slam into a cloud of matter [14]. Being close together on the sky is a correlation. To show cause, the team would need to connect the hidden jet's path to both the cloud and the hotspot. The team is already gathering more observations of the hotspot [15].
I think the identification is the stronger result. It rests on several instruments and an outside astronomer's endorsement [10][11]. For now, the accelerator idea rests on one object lying near one patch of sky [12][14].
What to watch
- The Astronomy & Astrophysics paper's distance estimate and its data from the three observatories, which will show how firmly IRAS 18293-0941 sits inside the galaxy.
- The team's new hotspot observations, and whether the hidden jet's path can be traced to the particle patch and a cloud of matter.
- Changes in the visible jet over days or weeks, the timescale Luque-Escamilla says a small black hole should show.