Analysis of the State-of-Art Telescopes: Hubble Space, FAST and

EHT

Zijun Wei

Department of Physics, Santa Monica College, 1900 Pico Blvd, Santa Monica, U.S.A.

Keywords: Telescopes, Hubble Space, FAST, EHT.

Abstract: As a matter of fact, telescopes are widely utilized in cosmology and astrophysics’ observations in recent years.

Various ambitious schemes for the telescopes are proposed and constructed with large size and high accuracy.

With this in mind, this study systematically analyses three among the most well-known telescopes, i.e., the

Hubble space Telescope, the Five Hundred Meter Aperture Spherical Telescope as well as the Event Horizon

Telescope. To be specific, the components, structures and functions of the three typical telescopes are

evaluated and introduced. At the same time, the advanced results observed in recent years by the facilities are

also demonstrated, including the observations of black holes from EHT. According to the analysis, the current

drawbacks for these facilities as well as the future developments for the telescopes fields are demonstrated

and discussed. Overall, these results shed light on guiding further development of various telescopes as well

as pave a path for further exploration of cosmology and universe.

1 INTRODUCTION

Telescopes have always been a significant instrument

in the universe. Ever since Galileo pointed his small

telescope towards the sky in 1609, telescopes have

greatly expanded the knowledge of the space

(Williams et al., 1996). Larger telescopes are required

for astronomers to see very remote and feeble sources

of light because they gather more light. Therefore,

building large telescopes has become crucial for most

of the astronomical discoveries (Freedman et al.,

2001). For instance, the Hubble Space Telescope

(HST) was launched in 1990 to provide much better

insights into stars, galaxies, and the rate of expansion

of the universe (Riess et al., 2022). Images taken by

Hubble were very sharp which enabled scientists to

measure distances accurately which in turn revealed

that the universe is expanding at a rate faster than

expected (Riess et al., 2022).

Over the last few years, several important

telescope projects have made considerable progress.

The James Webb Space Telescope (JWST), launched

at the end of 2021, began to produce science in 2022

(Astro2020 Decadal Survey, 2021). The JWST with

a 6.5-meter mirror Observes mainly in infrared

wavelengths which means that astronomers can look

at parts of the sky that are not observable with

previous telescopes. It has also provided pretty good

images of galaxies, star formation, and even the

atmospheres of exoplanets. These observations are

contributing to the knowledge of the early universe

and the search for life in the universe (Astro2020

Decadal Survey, 2021).

Another large project currently under

development is the Square Kilometre Array (SKA),

which will be the world’s largest radio telescope. The

SKA’s antennas are situated in Australia and South

Africa, and will be deployed such that they cover an

area of one square kilometre (Wedemeyer et al.,

2024). It will be able to pick up very faint radio

signals and enable scientists to investigate the state of

the universe right after the Big Bang. It will also solve

problems like dark matter, dark energy and galaxy

formation (Wedemeyer et al., 2024).

Alongside the space and radio telescopes, optical

telescopes are being built to be very large ground-

based telescopes. The European Extremely Large

Telescope (ELT) with a mirror of 39 meters in

diameter will increase the sensitivity to weak signals

from the celestial objects by a factor of 39 (European

Southern Observatory, 2022). The ELT is predicted

to assist in the finding of Earth like planets around

other stars and the formation of galaxies and stars.

Another telescope which is still under development is

the Atacama Large Aperture Submillimeter

152

Wei, Z.

Analysis of the State-of-Art Telescopes: Hubble Space, FAST and EHT.

DOI: 10.5220/0013815700004708

Paper published under CC license (CC BY-NC-ND 4.0)

In Proceedings of the 2nd International Conference on Innovations in Applied Mathematics, Physics, and Astronomy (IAMPA 2025), pages 152-157

ISBN: 978-989-758-774-0

Telescope (AtLAST) which is being developed to

observe stars and the sun at submillimeter

wavelengths. AtLAST will give new insights into the

stellar activity and the solar atmosphere and will

contribute to the knowledge of stellar formation and

evolution (Wedemeyer et al., 2024).

This paper is motivated by the recognition of the

importance of large telescopes in astronomy. These

powerful tools enable scientists to probe phenomena

that were heretofore unproblematized, solving long

standing mysteries while raising new questions about

the universe. For this, the paper is arranged as follows:

First, it defines what a telescope is, how it works and

what are the main types of telescopes, thus providing

the reader with a proper introduction. Second, it lists

the major applications of telescopes in astronomy and

emphasizes their role in science breakthroughs. Third,

the paper gives a detailed description of three specific

telescopes: Hubble Space Telescope, China’s FAST

radio telescope, and the Event Horizon Telescope

(EHT). It outlines what makes them special, what

contribution they have made to science and how they

have enriched the knowledge of the cosmos. Finally,

the paper outlines some current limitations of

telescope technologies, and looks ahead to future

developments, which could revolutionize astronomy

and how one will study the universe. In this

framework, the paper aims to argue for the need to

continue to invest in the development of telescopes

because these extraordinary machines help people to

understand the universe better.

2 DESCRIPTIONS OF

TELESCOPES

Astronomers use telescopes to view objects in space

by collecting and focusing electromagnetic radiation,

which includes visible light, infrared radiation, and

radio waves (Gardner et al., 2006). In general,

telescopes work by gathering more radiation than the

human eyes can gather and focusing it into a clear and

distinct image. The two primary principles through

which telescopes work are refraction and reflection.

Refracting telescopes use lenses to bend and focus the

incoming light while reflecting telescopes use mirrors

to collect and reflect radiation to a focal point.

Adapting to today’s large telescopes, mirrors are used

as these can be made to be much larger and more

efficient than lenses enabling astronomers to see very

faint and very distant cosmic objects (Gardner et al.,

2006).

Based on the kind of electromagnetic radiation

they detect, telescopes are also classified. Optical

telescopes, such as the Hubble Space Telescope,

observes visible light, and they are used by

astronomers to study galaxies, stars, and planets. The

James Webb Space Telescope (JWST) is an infrared

telescope that detects infrared radiation from objects

too faint, too cool, or too distant to see with visible

light alone (Gardner et al., 2006). Thus, infrared

telescopes are quite crucial in the study of early

galaxy formation, star formation processes and exotic

planets in other solar systems. Another major type is

radio telescopes, which capture radio waves from

space using large antennas or antenna arrays. The

Square Kilometre Array (SKA) will detect extremely

weak radio signals from distant cosmic phenomena

(Cordes, 2009). Radio telescopes allow astronomers

to study exotic objects such as pulsars, quasars, and

black holes, as well as explore the large scale

structure and evolution of galaxies.

The specific scientific objectives of different

telescopes are determined by their observational

potential. Optical telescopes have mainly contributed

to the advancement of the knowledge of stellar

properties, galaxy structures and planetary systems

round other stars. They are important in

understanding formation of stars, early universe

conditions and organic molecules (that may be an

indicator of life) by observing through cosmic dust

clouds. Black holes, fast changing cosmic events, and

the physics of extreme environments are examined

through mapping of cosmic background radiation

(Cordes, 2009).

In conclusion, of all the types of telescopes,

modern astronomy would not be complete without

them, and they are an indispensable tool in acquiring

the necessary information that helps shape the

understanding of the universe. The continuing

innovation in telescope technology holds the key to

new discoveries and a more profound understanding

of cosmic questions that remain unresolved (Gardner

et al., 2006; Cordes, 2009).

3 HUBBLE SPACE TELESCOPE

The Hubble Space Telescope is one of the greatest

achievements in astronomy and is one of the most

useful telescopes of the modern world. Launched in

1990, Hubble soars above the atmosphere, giving it

an unparalleled capacity to gather detailed images of

faraway objects without the blur caused by the

atmosphere (Williams et al., 1996). It has a primary

mirror that is 2.4 meters in width, a few smaller

Analysis of the State-of-Art Telescopes: Hubble Space, FAST and EHT

153

secondary mirrors, and a number of scientific

instruments that detect visible and ultraviolet light.

When objects in the distance shine or reflect light, the

radiation travels through space and strikes Hubble’s

primary mirror, which then reflects the light to a

smaller secondary mirror. The secondary mirror then

forms an image at the scientific instruments which

produce a sharp image or analyse the nature of the

object (Freedman et al., 2001).

The primary objectives of Hubble are to learn

about stars, galaxies, planets, and other objects in the

sky. It has scanned more than 1,000 galaxies, stars in

various states of their existence, planets in the solar

system and planets around other stars. This is

remembered for the “Hubble Deep Field” where

Hubble was turned to an apparently starless part of

the sky for many hours. Fig. 1 shows more than 3,000

galaxies, some up to fthe billion light-years away, a

gold mine for scientists to understand how galaxies

form and how the universe evolves (Williams et al.,

1996).

Figure 1: A color composite image of the full HDF field,

constructed from the F450W, F606W, and F814W images

(Williams et al., 1996).

Hubble has kept on finding out new things in the

recent past. This is because it has made a major

discovery on the Hubble constant, which is a measure

of the rate of the expansion of the universe. For this

purpose, Hubble has been used to measure the cosmic

distances using a type of star known as Cepheid

variables. These latest measurements are inconsistent

with the earlier theories, and this suggests that the

universe is expanding more rapidly than it should.

This discrepancy, termed the “Hubble tension,”

suggests that there is some new physics out there that

is not yet incorporated into the models (Riess et al.,

2022).

One of the most significant recent discoveries

made by Hubble is the existence of a distant star

called Earendel, which is about 12.9 billion light-

years away. It is a single star at such a great distance

that it is too dim to be detected directly. Nevertheless,

Hubble did it by taking advantage of a natural

magnifying effect known as gravitational lensing,

which is caused by massive galaxies along the line of

sight to Earendel. The discovery of Earendel gives a

rare opportunity to study stars from the early universe

and teach us about how they were born after the Big

Bang (Welch et al., 2022). These are just some of the

recent discoveries that highlight the continued

relevance of the Hubble Space Telescope. Hubble

was designed to be a well-built machine with a simple

working mechanism and excellent observing system

to enable scientists understand some of the most

important issues concerning the cosmos.

4 FIVE-HUNDRED-METER

APERTURE SPHERICAL

RADIO TELESCOPE

The Five Hundred Meter Aperture Spherical

Telescope (FAST), also referred to as the “China Sky

Eye”, is currently the largest single dish radio

telescope in the world. Situated in Guizhou Province

of China, FAST started full operation in 2020 and has

greatly enlarged the horizon of human vision in the

radio frequency region (Li et al., 2021). The telescope

has a 500 meter wide spherical mirror which is made

of more than 4000 mutually movable aluminum

panels. Unlike the normal fixed dish antennas, the

panels of FAST are able to change their configuration

in real time to generate a smaller and much more

accurate parabolic surface of about 300 meters in

diameter. This flexibility enables FAST to capture

celestial objects over a wider angle of the sky without

having to move the entire dish physically (Han et al.,

2021).

FAST works by picking up radio waves from far

away cosmic objects. The incoming radio signals

reflect on the large mirror and are focused on to a

platform receiver cabin which is suspended 140

meters above the dish. This cabin contains the

receiver elements that are sensitive to the incoming

signals and translate them into a form that can be used

for scientific analysis. Due to the fact that radio waves

from distant objects are very weak in intensity, it is

FAST’s large collecting area that enables it to detect

very weak signals which other smaller telescopes

cannot resolve well (Li et al., 2021).

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The fast pulsars, FRBs and neutral hydrogen gas

in distant galaxies are the main objects of research for

astronomers with the help of FAST. Pulsars are

compact stellar objects whose cores are neutron stars

that pulse out radioactive signals. FRBs are high

energy pulses of radio waves whose source lies

outside the galaxy. In analyzing the neutral hydrogen

gas, FAST enables investigators to determine how

galaxies have been created and transformed. This

makes it easy for FAST to look for signs of intelligent

extraterrestrial life through radio signals (Kang et al.,

2022).

It has been not so long ago that FAST has started

its work and already it has brought much research

output. One significant finding is the detection of a

large number of repeating pulses from the fast radio

burst FRB 121102. Within an observation period of

about 60 hours spread over several weeks, FAST was

able to identify more than 1,600 pulses from this

source. This discovery gave insights into the energy

content and the nature of FRBs and thus did not

support the earlier theoretical predictions which

suggested that the bursts are due to low efficiency,

high energy processes (Li et al., 2021).

Recently, there was another success, and it was

FAST’s precise observation of another repeating

burst, FRB 20201124A. Within two months of

observation, FAST observed about 1,800 bursts from

this object, which displayed some surprising behavior

in the polarization of the radio signal. This showed

that FRB 20201124A occurs in a medium with

dynamically evolving magnetic fields, which could

mean that it is associated with an X-ray binary or even

a magnetized stellar remnant. These observations

have helped to refine the knowledge of the process

and the environment of FRBs (Xu et al., 2022).

Successful surveys of neutral hydrogen gas have also

been done by FAST and hence new galaxies found.

These are so called “dark galaxies” which are rich in

gas but almost devoid of stars and therefore are

impossible to detect with optical telescopes. This

discovery gives important information on the early

formation and the subsequent evolution of galaxies

(Kang et al., 2022).

5 THE EVENT HORIZEN

TELESCOPE

The Event Horizon Telescope (EHT) is not a single

telescope, but a network of radio telescopes spread

around the globe. These telescopes work together to

observe space at very short radio wavelengths. EHT

creates a virtual telescope as large as the Earth itself

by combining observations from multiple telescopes.

Through Very Long Baseline Interferometry (VLBI)

astronomers obtain outstanding resolution power to

detect details beyond the capabilities of individual

telescopes (Event Horizon Telescope Collaboration,

2019).

The Event Horizon Telescope (EHT) functions

through coordinated observations of the same

celestial object from various positions on Earth's

surface. The participating telescopes independently

capture radio wave data from distant astronomical

objects. Scientists store the collected observations

with atomic clock-synchronized time information.

Scientists use powerful computers to merge data from

all telescopes after observations finish which results

in detailed images of the observed objects. The Event

Horizon Telescope uses its ability to observe black

hole event horizons to study environments near these

objects where gravity traps all light (Event Horizon

Telescope Collaboration, 2019).

EHT's main scientific goal is to observe and

image black holes, particularly their event horizons.

Black holes are among the most enigmatic objects in

the universe, and their intense gravity affects the

surrounding matter and radiation. Observing black

holes directly allows EHT to help scientists test

Einstein's General Relativity theory in the most

extreme gravitational conditions (Doeleman et al.,

2008).

EHT has obtained remarkable outcomes in its

recent operations. Scientists from the collaboration

published the world's first direct image of a black hole

which resides at the center of Messier 87 (M87) in

2019. Scientists observed a bright ring structure with

a dark central shadow through their instruments

which confirmed predictions from Einstein's theory.

The "black hole shadow" appears as a dark area

because the black hole's intense gravity traps all

incoming light. The ring of light surrounding the

shadow emerges from hot gas particles which orbit

near the black hole and produce radio waves before

reaching the event horizon as depited in Fig. 2 (Event

Horizon Telescope Collaboration, 2019).

The Event Horizon Telescope (EHT) achieved

another major milestone in 2022 by revealing the

first-ever direct visual evidence of Sagittarius A* (Sgr

A*) which serves as the supermassive black hole

located at the Milky Way's center. Scientists observed

a dark shadow surrounded by a bright ring of hot gas

in the same manner as the M87 black hole image. The

second direct observation proved that black holes of

any size follow identical behavior according to

Analysis of the State-of-Art Telescopes: Hubble Space, FAST and EHT

155

Einstein's theory of gravity (Event Horizon Telescope

Collaboration, 2022).

EHT has also studied the magnetic fields around

black holes. Polarized light observations of M87’s

black hole showed that there are strong magnetic

fields around the event horizon. These magnetic

fields are very important in determining the powerful

jets of material that are ejected from black holes.

Knowing these jets assist astronomers in

understanding how black holes affect their host

galaxies (Event Horizon Telescope Collaboration,

2021).

EHT has made these discoveries which have

greatly enhanced the understanding of black holes.

They show how human collaboration and advanced

technology can tackle some of the universe's deepest

mysteries, bringing previously invisible phenomena

clearly into view.

Figure 2: First M87 Event Horizon Telescope Results. I.

The Shadow of the Supermassive Black Hole (Event

Horizon Telescope Collaboration, 2019).

6 COMPARISONS

Different telescopes operate today with their own

distinct advantages and limitations. The Hubble

Space Telescope along with other optical telescopes

use visible light to produce precise images of distant

galaxies stars and planets. The study of galaxy

formation and universe expansion rates became

possible through their observational capabilities

(Williams et al., 1996; Riess et al., 2022). The

telescopes struggle to detect objects which are

obscured by space dust clouds. The instruments lack

sufficient ability to observe young stars and galaxies

that are blocked by dense dust clouds. The large size

of FAST allows it to detect signals which optical

telescopes cannot detect. The instrument has revealed

numerous enigmatic radio bursts together with

galaxies which were previously undetectable (Li et al.,

2021; Zhu et al., 2022). Radio telescopes lack the

capability to produce precise detailed images which

optical telescopes achieve. The images produced by

these instruments tend to have reduced resolution

which hinders researchers from studying tiny details.

The Event Horizon Telescope (EHT) combines

multiple radio telescopes to see extremely small

details. It captures clear images of black holes,

something no other telescope can do. For example,

EHT recently took the first pictures of black holes and

showed us what they really look like (Event Horizon

Telescope Collaboration, 2019; 2022). Nevertheless,

EHT can only observe very few objects, mostly black

holes, because its observations are complicated and

need telescopes around the world to cooperate at

exactly the same time.

Telescopes continue to face certain restrictions

despite their achievements. The atmosphere above

Earth prevents telescopes from Earth from making

complete observations. Space-based telescopes

eliminate this problem yet their high cost and

challenging maintenance requirements make them

difficult to operate. The current generation of

telescopes restricts scientists from observing objects

that are either too faint or too distant.

In the future, new telescopes might solve many of

these problems. Scientists are building bigger

telescopes on Earth, using special techniques to get

clearer pictures. New space telescopes like JWST will

observe infrared light, helping us see objects hidden

behind dust clouds (Gardner et al., 2006). New radio

telescope arrays like the Square Kilometer Array

(SKA) will become even more sensitive, letting us

discover things in the universe one can't imagine

today (Cordes, 2009).

7 CONCLUSIONS

To sum up, the exploration of the universe depends

heavily on large telescopes for scientific discovery.

This paper explained the fundamental principles of

telescopes by describing their operational

mechanisms and different types and functional

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156

applications. The Hubble Space Telescope together

with FAST and the Event Horizon Telescope

represent three essential telescopes in this discussion.

Through its clear images of distant galaxies Hubble

Space Telescope enabled scientists to study universal

expansion patterns. Scientists used FAST to detect

radio signals from space objects which led to the

discovery of new galaxies and unexplained radio

bursts. The Event Horizon Telescope produced

authentic black hole images which enabled scientists

to verify fundamental gravity principles. The current

limitations of telescopes include Earth's atmospheric

interference together with challenges in detecting

faint objects. The JWST and SKA telescopes

represent upcoming technological advancements

which will eliminate various current problems thus

enabling deeper space observation. The research

holds significance because advanced telescopes will

enable humans to solve basic questions about the

cosmic origins and universal operations. The ongoing

development of telescopes will enable us to discover

new universe information for multiple future years.

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