Black holes are one of the most powerful and mysterious objects ever studied. Light can't escape the surface of a black hole because of the extreme gravity involved. The study of these objects has traditionally been limited to observing their influence on objects and spacetime in their vicinity. The first image of a black hole was captured in 2019.
Scientists were able to see the bright ring surrounding the SMBH thanks to a technique known as Very- Long Baseline Interferometry. A new study shows how a space-based interferometry mission could reveal even more secrets within the veil of a black hole.
The research was led by a researcher with the Joint Institute for Very Long Baseline Interferometry European Research Infrastructure Consortium. He was joined by researchers from the Institute of Radio Astronomy (INAF), the Netherlands Institute for Space Research (SRON), the Flatiron Institute, and the Black Hole Initiative.
Ultra-high angular resolution in astronomy has always been seen as a gateway to major discoveries. Multiple observatories gather light from a single object that would otherwise be very difficult to resolve. Astronomers have relied on the detection of radiation at the millimeter and sub millimeter wavelength. Dr. Zsolt Paragi is a fellow researcher with JIVE ERIC.
“In general, high angular resolution imaging is achieved in astronomy in three ways: by increasing the size of our telescopes, observing light at shorter wavelengths, and eliminating (or at least compensating for) the disturbances caused by the Earth’s atmosphere.
“Radio astronomy pioneered the development of imaging techniques based on interferometry, when the signal from different telescopes at large distances are seamlessly (in our terminology: coherently) combined. In this case, the ultimate factor that determines the resolving power of the instrument is the distance between the telescopes, which we call baselines.”
The first image of a supermassive black hole was captured by the event horizon telescope. In 2021, there was an image of the core region of the Centaurus A galaxy and a radio jet. The light trapped within the event horizon was represented by faint circles in these images.
The shadows surrounding M87 were imaged for the first time, which constituted the confirmation of the existence of SMBHs. The infalling matter around the black hole is distorted by strong gravity. Dr. Paragi said that there have been developments in the field of VLBI that offer a glimpse of what's to come.
“Another keystone result in recent years was proving the cosmological origin of the mysterious, millisecond-duration radio flashes we call fast radio bursts. Due to its excellent high-resolution imaging capability, the European VLBI Network provided by far the highest accuracy sky localization of these very brief signals, that are extremely difficult to catch even with the most modern interferometers.
“These centimeter-wavelength images not only show which galaxy the signals come from, but they can also narrow down the position of the signal to small regions within the galaxy which will be crucial for the understanding of the phenomenon.”
The next logical step is to capture the Photon Ring. The force of gravity in this region is so strong that photons are forced to travel in the opposite direction. Much of the light from this ring was scattered before it reached Earth, creating the relatively blurred images in the EHT images. The next-generation EHT will add ten new telescopes while modernizing those already part of the network.
Astronomers will be able to provide the most detailed images of the photon rings around the SMBHs with the help of the space-based VLBI array. Gurvits, Paragi, and many of the team members wrote a white paper about the potential of a future space telescope known as the Terahertz Exploration and Zooming-in for Astrophysics.
The paper was submitted to the open call for large-class science mission proposals that will take place in the 20th century. The concept calls for a space-based interferometer to study the physics of spacetime in the vicinity of the SMBHs. It was described by Dr. Paragi.
“Observing from space at very short, mm to sub-mm wavelengths will open new dimensions to VLBI. The advantages of a mission based on the THEZA concept are two-fold. On the one hand, being able to go below the wavelengths the Event Horizon Telescope [or the ngEHT], a new population of supermassive black holes would be accessible for resolved black hole shadow imaging, which is obscured for those instruments. In addition, it would allow unique probes of black hole spin and spacetime properties as well.”
The telescope's elements were reviewed by the team, including antenna systems, receivers, low-noise amplifier, local oscillators, mixers, and data transport and processing. An interferometer based on the THEZA concept would achieve the three main goals of the astronomy mission. It will be free of interference from Earth's atmosphere and observe black holes at higher frequencies and longer baselines.
By studying unique systems consisting of close pairs of supermassive black holes, THEZA may reveal processes that led to an accelerated black hole growth at the dawn of the Universe. This will result in a better understanding of gravity, which is important because gravity plays a fundamental role in shaping the Universe.
Next- generation observatories will rely on improved detectors and data transmission technologies to provide a more detailed picture of some of the most mysterious objects in the Universe. The proposed Spektr-M space telescope is expected to launch by 2030. The primary mirror of this instrument will be able to observe the universe in the sub-millimeter to far-infrared wavelength.
As of late April, the James Webb Space Telescope was almost cold enough to conduct its own interferometry studies. As part of the Near-Infrared Imager and Slitless Spectrograph (NIRISS) instrument, the Aperture Masking Interferometer will turn the full amount of the mirrors into an interferometric array.
There are proposals to build telescopes on the far side of the Moon, as NASA plans to send astronauts back to the Moon. The future of astronomy is in space.
Further reading: arXiv
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