In the past century, black holes have transformed from being a mere curiosity into a key element of modern astronomy. Our understanding of black holes is now central to our understanding of the cosmos. The next generation Very Large Array (ngVLA) will help astronomers study these mysterious objects.
Astronomers have long known that Einstein’s theory of gravity allowed for an object to be so massive that light itself could not escape, but they initially doubted that black holes existed in the Universe. Today, however, black holes are recognized as a standard result of the death of very massive stars. The 2020 Nobel Prize in Physics was awarded for the study of the supermassive black hole at the center of the Milky Way Galaxy, and the link between supermassive central black holes to the formation and evolution of their host galaxies is a topic of active research.
A century ago, astronomers thought that the Universe consisted mostly of stars. They shine with the colors of light that our human eyes can see, and to most of us, the picture of an astronomer includes a telescope turned to the heavens. Today, however, we now recognize that a variety of objects shine at wavelengths that our eyes cannot see, from long wavelength radio waves to extremely high-energy gamma rays.
We now know that there are a variety of other messengers carrying to us information about the Universe. Cosmic rays are energetic sub-atomic particles, with energies well above those that particle accelerators such as the Large Hadron Collider can produce. In the most extreme cases, a sub-atomic particle can hit the Earth’s atmosphere with as much energy as a fast-pitch baseball. Billions of neutrinos rain upon us every second. They are born from nuclear fusion in the Sun, from distant exploding stars, from the regions near supermassive black holes. And gravitational waves constantly wash over the Earth and the Solar System. These distortions of spacetime itself are generated by colliding black holes, and potentially by the expansion of the Universe.
Within our own Milky Way, the ngVLA will greatly expand our ability to detect black holes in binary systems, enabling probes of supernova explosions and black hole formation. It will also enable the detection of less massive black holes that dwell in the centers of dwarf galaxies throughout the local cluster.
The detection of gravitational waves, along with their direct link to merging compact objects, marks one of the major breakthroughs in astrophysics over the past 10 years. The ngVLA will be able to resolve and observe the motion of mergers of supermassive black holes and neutron stars, both sources of gravitational waves. New facilities can detect these merging stellar remnants in galaxies up to 600 million light-years away through the gravitational wave and neutrino events they produce, and the ngVLA will be able to detect the radio emission to the same distance, permitting us to determine the physical conditions at the location of neutrino production.
Astronomers still have much to learn from black holes. In the near future, the ngVLA provide astronomers with a central tool for understanding black holes and multi-messenger astronomy.