<p><br>Galaxies are typically defined by their stars, yet not all of them glow. Some are composed largely of gas and dark matter, with little or no starlight to reveal their presence. The existence of these elusive objects, known as dark galaxies, has long been predicted by the Lambda Cold Dark Matter model, which describes how matter in the universe forms structures. Now, astronomers have identified 70 strong candidates for such galaxies using early observations from the Five-hundred-meter Aperture Spherical Telescope (FAST), with findings submitted to the arXiv preprint server on April 16. This work provides one of the most substantial catalogues yet of these elusive cosmic structures.</p><p>&nbsp;</p><h2><strong>What are dark galaxies</strong></h2><p><br>Most galaxies are visible across the universe due to the light from their stars. However, a rare category, low-surface-brightness galaxies, remains extremely faint. These systems contain very few stars and are largely dominated by dark matter, making them difficult to detect with conventional observations. NASA’s Hubble Space Telescope has identified CDG-2, a rare and nearly invisible ‘dark galaxy’ in the Perseus cluster, 300 million light-years away. Composed of roughly 99 per cent dark matter, it is one of the darkest known galaxies, identified by four faint globular clusters and a sparse, diffuse glow.</p><p>&nbsp;</p><p><strong>ALSO READ: </strong><a href="https://www.wionews.com/photos/india-s-thorium-push-top-7-countries-with-largest-reserves-and-where-india-stands-1777387216434"><strong>India’s thorium push: Top 7 countries with largest reserves and where India stands</strong></a></p><p>&nbsp;</p><h2>Why dark galaxies are expected to exist</h2><p><br>Theoretical models suggest that the universe should contain far more small dark matter halos than the number of observed galaxies. Many of these halos may never have formed stars. Processes such as ultraviolet background radiation from early quasars and galaxies can heat gas, preventing it from cooling and collapsing into stars. In other cases, the halos may be too small to retain the cold gas required for star formation. The result is a population of “missing” galaxies, dark matter-dominated systems that emit no visible light, often described as ghost-like structures.</p><p>&nbsp;</p><h2>Tracking hydrogen to reveal the unseen</h2><p>&nbsp;</p><p>According to sciencex.com, to identify these objects, researchers led by Marco Monaci analysed neutral hydrogen emissions detected by FAST. Hydrogen atoms emit a characteristic radio signal at a wavelength of 21 centimetres when their electrons change spin state. This signal serves as a reliable tracer of gas-rich systems, even when no stars are present. From 41,741 hydrogen sources in the FAST All Sky HI survey, the team narrowed their sample through distance limits and comparisons with optical catalogues. After several stages of filtering and visual inspection, they isolated 85 strong candidates, later refined to 70 after quality checks.</p><p>&nbsp;</p><p>&nbsp;</p><p><strong>ALSO READ: </strong><a href="https://www.wionews.com/photos/india-s-three-stage-nuclear-power-programme-what-is-thorium-and-how-it-could-shape-the-country-s-energy-future-1777383666108"><strong>India’s three-stage nuclear power programme: What is thorium and how it could shape the country’s energy future</strong></a></p><p>&nbsp;</p><h2><strong>What the discoveries mean</strong></h2><p><br>These 70 objects are not yet confirmed dark galaxies but represent the most promising candidates to date. They may include both truly starless systems and 'almost dark' galaxies with stars too faint for current detection methods. Confirmation will require deeper optical imaging and higher-resolution radio observations. As the FAST survey expands, researchers expect the number of candidates to grow to around 200, offering a crucial pathway to understanding galaxy formation and the role of dark matter in shaping the universe.</p>

The existence of these elusive objects, known as dark galaxies, has long been predicted by the Lambda Cold Dark Matter model, which describes how matter in the universe forms structures. 

Galaxies are typically defined by their stars, yet not all of them glow. Some are composed largely of gas and dark matter, with little or no starlight to reveal their presence. The existence of these elusive objects, known as dark galaxies, has long been predicted by the Lambda Cold Dark Matter model, which describes how matter in the universe forms structures. Now, astronomers have identified 70 strong candidates for such galaxies using early observations from the Five-hundred-meter Aperture Spherical Telescope (FAST), with findings submitted to the arXiv preprint server on April 16. This work provides one of the most substantial catalogues yet of these elusive cosmic structures. What are dark galaxies Most galaxies are visible across the universe due to the light from their stars. However, a rare category, low-surface-brightness galaxies, remains extremely faint. These systems contain very few stars and are largely dominated by dark matter, making them difficult to detect with conventional observations. NASA’s Hubble Space Telescope has identified CDG-2, a rare and nearly invisible ‘dark galaxy’ in the Perseus cluster, 300 million light-years away. Composed of roughly 99 per cent dark matter, it is one of the darkest known galaxies, identified by four faint globular clusters and a sparse, diffuse glow. ALSO READ: India’s thorium push: Top 7 countries with largest reserves and where India stands Why dark galaxies are expected to exist Theoretical models suggest that the universe should contain far more small dark matter halos than the number of observed galaxies. Many of these halos may never have formed stars. Processes such as ultraviolet background radiation from early quasars and galaxies can heat gas, preventing it from cooling and collapsing into stars. In other cases, the halos may be too small to retain the cold gas required for star formation. The result is a population of “missing” galaxies, dark matter-dominated systems that emit no visible light, often described as ghost-like structures. Tracking hydrogen to reveal the unseen According to sciencex.com, to identify these objects, researchers led by Marco Monaci analysed neutral hydrogen emissions detected by FAST. Hydrogen atoms emit a characteristic radio signal at a wavelength of 21 centimetres when their electrons change spin state. This signal serves as a reliable tracer of gas-rich systems, even when no stars are present. From 41,741 hydrogen sources in the FAST All Sky HI survey, the team narrowed their sample through distance limits and comparisons with optical catalogues. After several stages of filtering and visual inspection, they isolated 85 strong candidates, later refined to 70 after quality checks. ALSO READ: India’s three-stage nuclear power programme: What is thorium and how it could shape the country’s energy future What the discoveries mean These 70 objects are not yet confirmed dark galaxies but represent the most promising candidates to date. They may include both truly starless systems and 'almost dark' galaxies with stars too faint for current detection methods. Confirmation will require deeper optical imaging and higher-resolution radio observations. As the FAST survey expands, researchers expect the number of candidates to grow to around 200, offering a crucial pathway to understanding galaxy formation and the role of dark matter in shaping the universe.

<p>The existence of these elusive objects, known as dark galaxies, has long been predicted by the Lambda Cold Dark Matter model, which describes how matter in the universe forms structures.&nbsp;</p>

Why are some galaxies invisible? Astronomers identify 70 dark galaxy candidates with no visible stars using FAST

From NASA’s $10 billion James Webb Space Telescope to China’s giant FAST radio dish, the world’s most advanced telescopes are unlocking the universe’s deepest secrets. These incredible instruments capture light from the first galaxies and search for signs of life beyond Earth.

<p>From NASA’s $10 billion James Webb Space Telescope to China’s giant FAST radio dish, the world’s most advanced telescopes are unlocking the universe’s deepest secrets. These incredible instruments capture light from the first galaxies and search for signs of life beyond Earth.</p>

10 most powerful telescopes ever made

The world&#39;s largest single-dish radio telescope &#39;FAST&#39; began its operation in China today, state-run China Xinhua news reported.<br />
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The Five-hundred-meter Aperture Spherical Radio Telescope (FAST), made up of 4,450 reflecting panels and about the size of 30 soccer fields, &nbsp;would help in better understanding the origin of the universe and boost global hunt for extraterrestrial life, according to Indian news agency PTI.&nbsp;<br />
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Hundreds of astronomers and astronomy enthusiasts witnessed the official launch in a karst valley in Pingtang County.<br />
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&quot;FAST will enable Chinese astronomers to jump-start many scientific goals, such as surveying the neutral hydrogen in the Milky Way, detecting faint pulsars, and listening to possible signals from other civilizations,&quot; &nbsp;NAN Rendong, the general engineer and chief scientist of FAST had said before the launch.&nbsp;<br />
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<h5>FAST&nbsp;would help in better understanding the origin of the universe and boost global hunt for extraterrestrial life,</h5>
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Seventeen years after it was proposed, the work on nearly 1.15 billion-yuan (USD 180 million) project started by the National Astronomical Observatories of China (NAOC), under the Chinese Academy of Sciences (CAS) in 2011, according to PTI.&nbsp;<br />
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The telescope has been constructed in Dawodang in southeastern China&#39;s Guizhou Province, surrounded by karst formations that block radio frequency interference, according to the official website.&nbsp;<br />
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It has replaced Puerto-Rico&#39;s Arecibo Observatory in not just size but features as well with &nbsp;&quot;larger sky coverage, with a light-weight, high precision feed cabin which can be adjusted,&quot; according to official sources.&nbsp;<br />
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The telescope has been constructed from thousands of differently shaped segments in a &quot;cable-net structure, comprisingof thousands of steel cables, nodes and corresponding driving cables, which are tied to actuators on the ground,&quot; forming a parabolic surface.&nbsp;<br />
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Interestingly, just two days before the telescope&#39;s big operational launch, &nbsp;reknowned Stephen Hawking in a 25 minute film cautioned from contacting aliens.<br />
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&quot;Our first contact from an advanced civilisation could be equivalent to when Native Americans first encountered Christopher Columbus and things &ldquo;didn&rsquo;t turn out so well&rdquo;, The Guardian quoted him saying.&nbsp;<br />
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(WION with inputs from agencies)&nbsp;<br />
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The Five-hundred-meter Aperture Spherical Radio Telescope (FAST) is the size of 30 soccer fields and is made up of 4,450 reflecting panels

The world's largest single-dish radio telescope 'FAST' began its operation in China today, state-run China Xinhua news reported. The Five-hundred-meter Aperture Spherical Radio Telescope (FAST), made up of 4,450 reflecting panels and about the size of 30 soccer fields, would help in better understanding the origin of the universe and boost global hunt for extraterrestrial life, according to Indian news agency PTI. Hundreds of astronomers and astronomy enthusiasts witnessed the official launch in a karst valley in Pingtang County. "FAST will enable Chinese astronomers to jump-start many scientific goals, such as surveying the neutral hydrogen in the Milky Way, detecting faint pulsars, and listening to possible signals from other civilizations," NAN Rendong, the general engineer and chief scientist of FAST had said before the launch. FAST would help in better understanding the origin of the universe and boost global hunt for extraterrestrial life, Seventeen years after it was proposed, the work on nearly 1.15 billion-yuan (USD 180 million) project started by the National Astronomical Observatories of China (NAOC), under the Chinese Academy of Sciences (CAS) in 2011, according to PTI. The telescope has been constructed in Dawodang in southeastern China's Guizhou Province, surrounded by karst formations that block radio frequency interference, according to the official website. It has replaced Puerto-Rico's Arecibo Observatory in not just size but features as well with "larger sky coverage, with a light-weight, high precision feed cabin which can be adjusted," according to official sources. The telescope has been constructed from thousands of differently shaped segments in a "cable-net structure, comprisingof thousands of steel cables, nodes and corresponding driving cables, which are tied to actuators on the ground," forming a parabolic surface. Interestingly, just two days before the telescope's big operational launch, reknowned Stephen Hawking in a 25 minute film cautioned from contacting aliens. "Our first contact from an advanced civilisation could be equivalent to when Native Americans first encountered Christopher Columbus and things “didn’t turn out so well”, The Guardian quoted him saying. (WION with inputs from agencies)

World's largest radio telescope begins operations in China

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Why are some galaxies invisible? Astronomers identify 70 dark galaxy candidates with no visible stars using FAST

10 most powerful telescopes ever made

World's largest radio telescope begins operations in China