Fill in the blanks in the parameter space of observational astronomy

In observational astronomy, we essentially measure the location, flux density (at some frequency and some time), distance, and angular size of the sources. We can construct a parameter space of observational astronomy with the parameters, such as the sample size of sources, frequency (bandwidth and frequency resolution), time (observing length and time resolution), sensitivity, and angular resolution of the telescope. We would always obtain new knowledge of the universe with instruments that fill in the blanks in the parameter space, eg, telescopes used for better surveys (which enlarge the sample sizes of sources) and telescopes with higher sensitivity, angular resolution, frequency resolution, or time resolution.

In the year 2022, there has been rapid progress in observational astronomy. Astronomers have filled in part of the blanks in the parameter space with telescopes of higher sensitivity, instruments in a new frequency range, and a larger sample of stars from survey telescopes.

James Webb Space Telescope (JWST) observations generated images of galaxies (see Figure 1), galaxy clusters, and star-forming regions with unprecedented detail compared with that obtained with the Hubble Space Telescope. Since the JWST performs observations with unprecedentedly high angular resolution in the infrared band, it reveals structures largely obscured in the optical band of the Hubble Space Telescope. The JWST also detected some very high-redshift galaxies for the first time, providing information on galaxy evolution in early times.

Figure 1.

The Image of Stephen’s quintet taken by JWST and the Solar Hα image taken by the Chinese Hα Solar Explorer

(A) Stephen’s quintet taken by JWST (from NASA, ESA, CSA, and STScI).

(B) Solar Hα image taken by the Chinese Hα Solar Explorer (from NJU and CAS). It is the first ever solar Hα imaging observation from space.

The maximum sample of stars measured by the astrometric satellite Gaia and the Large Sky Area Multi-Object Fiber Spectroscopic Telescope makes it possible to study the early formation history¹ of our Milky Way for the first time.

Following detecting the photon with energy exceeding 1 PeV for the first time in 2021, the Large High Altitude Air Shower Observatory detected several thousand photons at 18 TeV from a gamma-ray burst (GRB), GRB221009A. It is the first time that photons with energy exceeding 10 TeV in a GRB have been detected, providing new information about these bursts.

The observations of fast radio bursts (FRBs) with the Five-Hundred-Meter Aperture Spherical Radio Telescope and other telescopes have found a complex environment of FRBs and given constraints to the ambient magnetic² field of FRBs. There is hope that we will finally reveal the nature of FRBs soon.

Following the Chinese Hα solar explorer (achieving the first ever solar Hα imaging observation from space; see Figure 1 for the image it took) launched in 2021, a new space solar satellite, the Advanced Space-based Solar Observatory was launched on October 9, 2022. The best-quality images and videos from the Advanced Space-based Solar Observatory will be released in about 6 months and kept updated.

Since the universe has a finite age and the speed of light (also other messengers, eg, neutrino and gravitational wave) is also limited, we can only observe a finite part of the whole universe, ie, the observable universe. In the observable universe, the number of galaxies is finite. We can only obtain samples with a finite number of sources. Due to the uncertainty relation Δν·Δt ≥ 1 (where we have eliminated Planck’s constant), we can only obtain limited frequency resolution and time resolution simultaneously. The angular resolution is also limited (∼several micro-arcseconds) because of the scattering of electromagnetic waves by the interstellar medium and the lensing by intervening objects.³ Apparently, the parameter space of observational astronomy is finite in most dimensions. The possible exception is the observation time.

With the development of sophisticated instruments, we may finally reach the boundary of the parameter space in most dimensions. However, there are still large blanks in the parameter space. For example, we have touched the angular resolution limits in the radio band with the very long baseline interferometry technique. There are more than three orders of magnitude to the upper limits in the optical, infrared, and higher energy bands.³ We should still plan for larger telescopes to fill in the blanks in parameter space to obtain new knowledge of the universe. Besides larger telescopes, it is also necessary to build survey telescopes to observe more sources, based on the success of the Sloan Digital Sky Survey. The atmosphere is only transparent to radio, optical, and several infrared bands. We will still face challenges from the increasing number of satellites, eg, Starlink. Therefore, we should build large survey space telescopes to achieve the best stability and angular resolution. This is the idea of the Chinese Space Station Telescope, which will launch in the coming years. Large survey space telescopes in other bands will also help to fill in the blanks in the parameter space.

Even when we finally reach the boundary of the parameter space in most dimensions, we still need to continue our observations. To demonstrate this point, let us look at two examples. First, in the past, humans observed the sky with naked eyes for thousands of years. We have not explored the parameter space in most dimensions, but the observation time is getting longer. Numerous transient phenomena, such as novae and supernovae, are recorded with their observations. These records help us determine the exact age of the Crab pulsar. Second, in solar physics, there is only one object to observe, but we are constantly obtaining new insights with continuous observations of the sun. When we reach the boundary of the parameter space, the paradigm of traditional observational astronomy will change.

Astronomy would become the continuous observations of several or all observable objects. In the era of constantly monitoring a large sample of sources, astronomy will become a kind of data science. Data storage and access would become the bottleneck of observational astronomy. We should be able to conveniently access the data obtained over tens of years, even hundreds of years. We still lack the corresponding infrastructure and mechanism to support these practices, although we already have virtual observatories. There is still a long way to make this happen.

Astronomy may also become a special kind of chemistry and biology to study the evolution of molecules and the origin of life. We have already seen this trend nowadays. When we look at chemistry and biology, we always find endless new states and new patterns of molecules. Similarly, in astrochemistry or astrobiology, the structure of the parameter space would be different. We may never go reach every corner. There will always be blanks to fill in.

Published Online: January 2, 2023