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Tuesday, October 20, 2026

 

On violence in fighting occupation: The case of Palestine

October 7 Israeli tank Palestine flag

First published at New Politics.

Author’s note: The following text is a postscript, dated February 22, 2026, to recent editions — Arabic, German, and Spanish — of my 2025 book, Gaza Catastrophe: The Genocide in World-Historical Perspective. The postscript discusses Palestinian liberation strategy and its various manifestations since the completion of the Israeli occupation of Palestine in 1967. In this regard, it is important to bear in mind the results of the most recent public opinion poll conducted in Gaza and the West Bank on August 20–25 by the Jerusalem Media and Communications Centre (JMCC). Asked about the “best method to achieve the Palestinian people’s goals of ending the occupation and establishing a state,” only 13.3% chose “military means” (9.7% in Gaza and 15.7% in the West Bank), while 17.8% were in favor of “non-violent resistance,” and a majority of 55.8% in favor of “peaceful negotiations.” This bears witness to the degree of exhaustion of the population of the 1967-occupied Palestinian territories, with 58.6% trusting no Palestinian personality and 55% trusting no political faction. Rebuilding a sustainable Palestinian popular emancipatory struggle in those territories will require a lot of patient effort.


The farther we move from what has befallen the Palestinian people since the Hamas-led operation on October 7, 2023, the clearer becomes the magnitude of the disaster triggered by what I have described as “the most catastrophic miscalculation ever in the history of anticolonial struggle.” Seizing the opportunity provided by that fateful operation and the apparent war crimes that it involved, the far-right government of Israel felt unrestrained, even widely supported, in launching the most murderous and devastating war ever waged against the Palestinian people — one that has rightly been recognized as genocidal by many scholars, human rights organizations including the well-known Israeli organization B’Tselem, and various international bodies.

The massive death toll and the total human cost resulting from Israel’s onslaught, the full extent of which won’t be known for some time, are compounded by the unprecedented intensity of destruction of all means of life in the Gaza Strip: buildings, infrastructure, natural environment. The main aim of this mass destruction is the forced displacement of the Gazan population, i.e. the furthering of the ethnic cleansing of the land of Palestine between the Jordan River and the Mediterranean Sea that has been core to the Zionist settler-colonial enterprise since the foundation of the State of Israel in 1948. In parallel, creeping ethnic cleansing and annexation have intensified to an unprecedented level in the West Bank.

Consequently, the Palestinian people are farther from self-determination today than at any time since the unarmed popular uprising, known as the First Intifada, that started in December 1987 in the territories seized by Israel in the June 1967 war, i.e. the West Bank and Gaza, usually designated as the Occupied Palestinian Territories (OPTs). The Palestinian movement now faces a long period of retreat under duress. In this most tragic period of its history, the question of how it can secure its survival and go on to fight back with any chance of success must be prioritized.

Stages of struggle

The assessment must necessarily start from the peak impact that the Palestinian people’s struggle achieved in the late 1980s. Indeed, the Intifada provoked a deep crisis in Israel’s society, polity, and military. A strong opposition to the continued occupation of the OPTs emerged. The “Labor” wing of Zionism came back to power in 1992, defeating the Zionist far-right Likud party. They engaged with the Palestine Liberation Organization (PLO) — which Israel had hitherto castigated as “terrorist” — in the negotiations that led to the 1993 Oslo Accords.

The Israeli army withdrew from the densely populated areas of the 1967-occupied Palestinian territories and handed rule over them to the PLO-based Palestinian Authority (PA). But the PLO leadership had committed the major error of not insisting on including in the accords the freezing of settlements. This issue led to the collapse of the Oslo “peace process” by the end of the century. The expansion of Zionist settlements and the increase in oppressive measures against the Palestinian population led to growing popular anger that the Islamic fundamentalist Hamas (Arabic acronym for the Movement of Islamic Resistance, originally a branch of the Muslim Brotherhood) capitalized on by waging a series of indiscriminate suicide attacks against the Israelis. This contributed to renewed polarization through which Israel’s society and polity shifted back rightward.

It is against this background that the PLO leadership made another major error in what was called the Second Intifada, in allowing for the use of the light weapons that the Israeli occupation had authorized PA troops to possess for the purpose of policing the Palestinian population. This episode started in the autumn of 2000 in response to the provocation staged by rightwing Zionist leader Ariel Sharon at the Al-Aqsa compound in Jerusalem and in protest against the betrayal of the hopes created seven years earlier. The effect, however, was the opposite of that of the First Intifada. The Second Intifada saw the return of Likud to power under the leadership of Sharon — the military commander of Israel’s invasion of Lebanon in 1982 and the man condemned for his role in supervising the horrible massacres at the Sabra and Chatila camps in Beirut. This was followed in 2002 by the most violent Israeli onslaught on the OPTs until that year.

Since then, a much-crippled Palestinian Authority has ruled part of the OPTs under the thumb of the Israeli occupation. Benefiting from popular disgust with the PA’s subservience and corruption, Hamas won the Palestinian parliamentary election of 2006. Clashing with the PA, which refused — with Western encouragement — to abide by the election’s outcome, Hamas took over Gaza in 2007, two years after Israel’s withdrawal from the Strip, leading to a partition of the semi-autonomous parts of the OPTs. Today, Hamas’s semi-autonomous government of Gaza under Israeli oversight has been wiped out, most of the Strip has been reoccupied by Israel, and a quasi-colonial administration is being put in place in the remaining part under the direct supervision of U.S. president Donald Trump in person. The PA, in turn, is under intense pressure from the United States to abide by Israel’s requirements in furthering its subservience to occupation authorities.

The setback from the aftermath of the First Intifada until today’s disastrous state of affairs for the Palestinian people is enormous. This series of defeats of armed struggle episodes, after the major success achieved by an unarmed popular uprising, provides clear and important lessons for the Palestinian struggle, stemming from a general strategic reflection on struggles against foreign occupation with regard to the means they resort to. This is a pragmatic discussion: except for war crimes, such as the deliberate killing of children and non-combatants, armed resistance to foreign occupation is an undisputable right in international law. Whether violent means are effective in each specific case, however, is another question entirely. Here again there is no general rule: the history of struggle against colonial domination and foreign occupation has witnessed successful cases of each of violent and non-violent struggles, as well as of combinations of both.

Liberation strategies

When a foreign army occupies a land whose population is hostile to it and from where withdrawal is an option for the invader, a great imbalance in military strength can be successfully compensated by asymmetric means, such as guerilla operations harassing the occupying army, in order to bring it to conclude that the cost of continuing occupation is higher than whatever benefit is derived from it. This dynamic is very much compounded by the ability of the liberation struggle to win over the minds, if not the hearts, of a major section of the aggressor country’s population.

The Vietnamese resistance against U.S. occupation, combined with the antiwar movement in the United States, achieved that result in 1973. The Lebanese resistance to Israeli occupation achieved it in 2000 on a background of opposition by a significant portion of Israel’s population to continued occupation. When the Israeli army was occupying the densely populated areas in the OPTs from 1967 until 1993, guerilla attacks harassing it made strategic sense. Ultimately, however, it was the non-violent Intifada and its impact on the Israeli population that proved decisive in getting Israel’s military to favor withdrawal from those areas, leading to the Oslo Accords.

The situation is fundamentally different when confronting a state entrenched in a territory that it sees as its one-and-only land, inhabited by a population that overwhelmingly sees that state’s armed forces as their own. There is no way under such circumstances to compensate for the enemy’s overwhelming military superiority by asymmetric military means: it is not going to surrender or withdraw its forces under the impact of transborder guerilla attacks. Indeed, it will rather retaliate with all the power of its superior military to achieve deterrence, inflicting brutal devastation on the attackers’ territory to deter them from repeating their attacks.

Thus, when Hezbollah carried out a guerilla operation across Lebanon’s border with the Israeli state in 2006, it was met with devastating retaliation that destroyed whole areas inhabited by its sectarian-cum-political popular constituency. Never again did Hezbollah resort to such cross-border attacks. Yet, when it launched a self-limiting bombing exchange with Israel in solidarity with Gaza in October 2023, it eventually paid a huge price, with Israel decapitating the organization and destroying much of its military capabilities a year later. Hezbollah had believed that it had accumulated enough deterrent means — rockets and missiles provided by Iran after 2006 — to keep the mutual bombing within limits. This proved to be a fatal miscalculation.

Hamas’s miscalculation in October 2023 was far worse, in that its consequences have been much more dreadful. In October 2023, Israel had been governed for less than a year by the most extreme far-right coalition in its history, the farthest to the right of any freely elected government in the world — a coalition that included openly racist groups advocating the annexation of the OPTs and expulsion of their population. To any rational assessment, it was obvious from the very morning of October 7 that Israel’s retaliation would be hugely murderous and devastating, way beyond anything it had done in all its many wars since its foundation in 1948. For anyone concerned, unlike Hamas, with the strategic impact of the Palestinian struggle on the Israeli population, it was obvious likewise that the effect of the attack would be a massive swing toward the most extreme hatred of Palestinians.

Breaking the Zionist consensus

What, then, could a rational and efficient perspective for Palestinian liberation consist of? Given the realities on the ground, it should necessarily involve a strategy of popular struggle aimed at dividing Israeli society and changing Israeli politics. Despite the growing hegemony of the extreme right, Israel’s political regime is still based on proportional electoral representation of its citizens, one-fifth of whom are Palestinian citizens of Israel (PCI). This means that, were about two-fifths of Jewish Israelis to be convinced of the need to end the occupation of the 1967 territories and accept Palestinian rights, this would be enough to provoke a major rupture of the Zionist consensus.

For years, however, the Palestinian resistance in the OPTs has been torn between subservient collaboration on the part of a PA relying upon Arab and international pressure on Israel to improve its lot, and armed confrontation led by Hamas, consisting in successive rounds during which Israel would confront Hamas’s low-tech rockets with much more murderous and destructive bombing. None of the two Palestinian administrations — neither the PA in the West Bank nor Hamas in Gaza — have shown the least interest in addressing the Israeli population and winning over a significant section of it to the support of Palestinian rights. Both remain deeply suspicious of any alliance with political forces independent from them — be they Arab or Jewish or, most importantly, mixed – within Israel’s pre-1967 boundaries, and fear losing control of the territories under their administration, a control that is very much antithetical to the type of local self-organization that was the First Intifada’s strength at its peak in 1988. New initiatives toward popular mobilization only came from the grassroots of Palestinian society, pointing to what kind of popular resistance is possible.

In March 2018, independent activists in Gaza initiated what they called the Great March of Return, i.e. weekly demonstrations toward the fence surrounding the Strip. This went on powerfully for a year and then continued with a reduced impact until the end of 2019. The initial popular success of that endeavor led the Hamas leadership to take control of it and steer it toward a deal with Benjamin Netanyahu’s government in March 2019, easing the blockade imposed on Gaza and allowing an increase in Qatari funding of the Hamas administration. This cooptation, along with Israeli forces’ murderous firing on the marchers (over 200 killed and thousands injured between March 2018 and March 2019), the setting of an unrealistic goal (the implementation of the Palestinian refugees’ right of return to their 1948 territory of origin), and most crucially the lack of simultaneous similar mobilization in the West Bank, where neither the PA nor Hamas favored extending it, ultimately curtailed the effectiveness of the endeavor. Nevertheless, it demonstrated what kind of pressure mass, non-violent resistance can unfold.

The next significant experience was more spontaneous. It was the beginning in May 2021 of a popular uprising in the West Bank, as well as among Palestinian citizens of Israel, ignited by the eviction of Palestinians in the Sheikh Jarrah neighborhood of East Jerusalem. The important popular mobilization that unfolded within a few days was stifled by Hamas’s interference, when it started launching rockets from Gaza, thus initiating an exchange of bombing that resulted, as usual, in many more Palestinian casualties than Israeli, and quickly dampened the popular uprising’s momentum. What we have seen over the last two-and-a-half-years in Gaza represents a catastrophic culmination of the same pattern.

In the face of the present disaster, it is to be hoped that the Palestinian people will find its way to new popular non-violent resistance struggle throughout the OPTs, in order to mobilize maximum international pressure as well as split off at least a significant minority of Israel’s Jewish population from the Zionist consensus. Only by such struggle, combined with international solidarity and the global Boycott-Divestment-Sanctions (BDS) movement, the natural complement of a non-violent popular strategy, can Palestinian rights be efficiently asserted. This prospect is reinforced by the surge — in reaction to the Gaza genocide — of Palestine solidarity in Western countries, including the United States, and most crucially among American Jews, especially the younger generations. Continuing to resort to reactive violence — however legitimate and humanly understandable it is, especially after the Gaza genocide and in the face of ever more brutal aggression against the Palestinian population in the West Bank — would inevitably be used as a pretext by Israel and its U.S. sponsor, now the quasi-colonial overseer of Gaza, to unleash yet more mayhem with a view to speeding up the ethnic cleansing of Palestine.

Gilbert Achcar grew up in Lebanon and has lived and taught in Paris, Berlin, and London. He is Professor Emeritus at SOAS, University of London. His many books include The Clash of Barbarisms (2002, 2006); Perilous Power: The Middle East and US Foreign Policy, co-authored with Noam Chomsky (2007); The Arabs and the Holocaust: The Arab-Israeli War of Narratives (2010); Marxism, Orientalism, Cosmopolitanism (2013); The People Want: A Radical Exploration of the Arab Uprising (2013); Morbid Symptoms: Relapse in the Arab Uprising (2016); The New Cold War: The United States, Russia, and China from Kosovo to Ukraine (2023); and Gaza Catastrophe: The Genocide in World-Historical Perspective (2025).

Thursday, October 01, 2026

Bass and Raman split on Gaza and the term genocide during Jewish Federation forum

David Zahniser, Noah Goldberg
Wed, September 30, 2026 


From left, Los Angeles City Councilmember Nithya Raman and Mayor Karen Bass.
 (Los Angeles Times)

The candidates for Los Angeles mayor gave opposing takes on the war in Gaza on Tuesday night, with Councilmember Nithya Raman saying Israel has committed genocide and Mayor Karen Bass asserting the term is inappropriate.

Appearing back to back at the Skirball Cultural Center, Bass and Raman both said they would fight to keep L.A.'s Jewish residents safe.

But Raman faced a spate of questions about her sit-down interview with leftist Twitch streamer Hasan Piker, a vehement critic of Israel, and her support from Democratic Socialists of America, which has called for the boycott of and divestment from Israel over its treatment of Palestinians.

Moderator Alex Cohen, seated next to Raman onstage, asked the council member to explain her decision to portray Israel's actions as genocide, calling it a "highly inflammatory term."

Raman said she turned to international experts — including some Israeli experts — to make her decision.

"That is what guided me to using that term in describing what's happening in Gaza," she said. "I used it because I felt compelled to speak out about issues that we saw, and images that are coming, the targeting of hospitals, the deaths of children."

The two candidates gave their remarks during a forum hosted by Jewish Federation Los Angeles and other groups, which focused on issues important to Jewish Angelenos.

Once Bass took the stage, Cohen posed the Gaza question a second time, asking whether the mayor views the term genocide as appropriate.

"When I think of foreign affairs, especially conflicts, my focus is on how they impact the city of L.A. — and no, I don't," Bass responded.

Bass said the schools she attended growing up had many Jewish students whose parents or grandparents were Holocaust survivors.

"My job is to keep Angelenos safe, and I think there is a lot of divisiveness that happens, and I don't want to see that happen at all," she said.

The war in Gaza began in 2023, when Hamas-led militants attacked Israel, killing around 1,200 people and kidnapping 251. Israel's resulting counteroffensive has resulted in 74,000 Palestinian deaths, according to figures issued by the Gaza Health Ministry.


The death toll has sparked condemnation from global leaders and from human rights organizations. Israeli Prime Minister Benjamin Netanyahu, speaking at the U.N. last week, said assertions that Israel engaged in genocide were "the biggest lie of the century."

Genocide is considered an international crime. In the wake of the Holocaust, a United Nations convention has been defined as actions that are committed with the intention of destroying — in whole or in part — a national, ethnic, racial or religious group.

Raman has been endorsed by Democratic Socialists of America, which censured her in 2024 for seeking and accepting the endorsement of Democrats For Israel-Los Angeles, a Zionist group. Asked about her decision to accept the endorsement, Raman told Piker in May: "I wouldn't seek it out now."

Cohen, the forum's moderator, told Raman her that her appearance on Piker's program was "deeply hurtful" to many "considering what Piker has said in the past about Jews."

"You told ABC News, and I quote, that you 'vehemently disagree' with some of his statements," Cohen said. "And yet that disagreement did not appear during that interview. We'd like to ask what specifically drove your decision to appear on his program, and were you concerned in any way, shape or form that it could signal to Angelenos an endorsement of many of his views?"

Piker has been accused of making antisemitic remarks, including calling ultra Orthodox Jews "inbred," which he later said he regretted.

Raman said she has repeatedly spoken out against antisemitism, and was the first elected official at City Hall to denounce the October 2023 attack on Israel.

On her interview with Piker, she wanted to reach voters on a wide range of platforms, particularly at a time when young voters don't watch television news.

"It's important for us as elected officials, as people running for office, to go and speak to them even when you disagree with parts of those individuals' [views]," Raman said.

The two candidates offered different assessments of BDS, the Boycott, Divest and Sanction movement targeting Israel over its treatment of Palestinians. Raman called the movement "a legitimate form of peaceful protest."

"And I support people's right to protest," she said. "I will fight for that right even when I don't agree with protesters, or when I agree with protesters."

Raman also noted that she does not have BDS as part of her platform.

Bass said she would oppose legislation that seeks to enact BDS at CIty Hall.

"If it came before the city council — it depends on what it is," she said. "But if it was calling for that I would oppose it."

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This story originally appeared in Los Angeles Times.

Tuesday, September 29, 2026

SPACE/COSMOS

Canadian telescope directly maps earliest glow of hydrogen, opening a new window on the universe



University of British Columbia
A view of CHIME at night, with the Milky Way in the background

image: 

A view of CHIME at night, with the Milky Way in the background

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Credit: CHIME collaboration




The Canadian Hydrogen Intensity Mapping Experiment (CHIME) has shown, for the first time, that it can detect the faint glow of hydrogen gas from deep in the universe's past using only its own data.

The breakthrough paves the way for a faster, less expensive method for scientists to study dark energy — the mysterious force thought to be driving the universe to expand at an ever-increasing rate, and one of the biggest open questions in physics. The achievement also marks a milestone for the telescope, built for this very reason. The findings are published in a paper today in The Astrophysical Journal.

“Hydrogen is the most common element in the universe and the raw material from which stars form,” said co-author Dr. Arnab Chakraborty, postdoctoral fellow at the University of Toronto who first proposed the finding. “Its faint radio emission acts like a cosmic tracer, revealing how matter is distributed across space.”

There are contradicting theories about the nature of dark energy in the astrophysical community. Using its own data, CHIME can investigate these theories independently and help prove or disprove them.

“This is a completely new technique for probing the cosmos, delivered by an instrument that was conceived, built and funded by Canadians,” said co-author Dr. Mark Halpern, professor in the UBC department of physics and astronomy and CHIME principal investigator. “It’s a bold new step in the global cosmology program and a Canadian success story.”

Mapping hydrogen’s glow

CHIME is a radio telescope near Penticton, British Columbia, hosted by the National Research Council of Canada (NRC), which maps the entire northern sky every day.

It is a pan-Canadian research project built and operated by scientists at the University of British Columbia, McGill University, the University of Toronto and the Dominion Radio Astrophysical Observatory (NRC), as well as other North American collaborators including Arizona State University.

CHIME was built to map the distribution of hydrogen gas in the early universe, allowing astronomers to calculate its expansion and thus investigate dark energy, the mysterious force thought to be driving the universe to expand faster over time.

Previously, CHIME had to cross-correlate its observations with galaxy survey data from other telescopes. Galaxy surveys investigate the same question, using light and focusing in fine detail.  They cost millions more dollars, and they focus just on the part of the universe hot and dense enough to form stars.

By mapping the combined radio glow that hydrogen emits on its own, CHIME can explore the same questions at a greater scale, further back in time, at a fraction of the cost and without relying on anyone else’s results.

Signal interpretation

In an accompanying paper, the researchers examined what the observed signal reveals about the distribution of hydrogen in the universe.

“Our data indicate that roughly two per cent of the hydrogen in the universe was in neutral atomic form at this time, broadly consistent with other measurements” said co-author Dr. Shabbir Shaikh, postdoctoral fellow at Arizona State University. “By measuring how that hydrogen is distributed and clustered, CHIME gives us a new way to test our understanding of how galaxies form and evolve”.

Delayed celebration

The finding wasn’t a Eureka moment. The research applied new data analysis and processing techniques to find the faint signal amongst the overwhelming noise of the background universe, human technology and even the instrument itself. They then spent more than a year testing the finding to prove it was correct: it was indeed a call from the universe itself when it was about five billion years old, based on 94 nights of observation data collected in 2019.

“We worked very hard to convince ourselves that this wasn't a false alarm,” said Dr. Chakraborty. “After all the tests, the signal remained. That gave us confidence we were seeing real hydrogen from the distant universe.”

Seven years of data

The current measurement uses only a small fraction of the data CHIME has collected since operations began. Researchers now have nearly seven years of observations available and are working to expand the analysis to include earlier periods in cosmic history when the universe was only three billion years old. 

This project is funded by the Canada Foundation for Innovation, the National Research Council of Canada, the Natural Sciences and Engineering Research Council and the provinces of British Columbia, Ontario and Quebec, and supported by the Digital Research Alliance of Canada.

Additional quotes:

 

“For a long time, astrophysicists have believed there is great potential in this hydrogen mapping technique with this kind of telescope. By actually showing that the technique works in practice, we've opened up a whole new window on the universe. We can use it to test our current theories, and learn new things about galaxies and other properties of the universe.”

-       Co-author Dr. Simon Foreman, assistant professor at Arizona State University

ASU astronomers uncover black hole jets reaching far beyond their galaxies and deciding their fate




Arizona State University
Black Hole Jets

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Artist’s illustration of a supermassive black hole at the center of a radio galaxy launching powerful jets (shown in pink) all the way into the galaxy’s CGM. The study finds that these jets do not light up the surrounding gas equally in all directions. Instead, the hydrogen gas glows (shown in red) most strongly along the path of the radio jets. This suggests that black holes can send energy far beyond the galaxy’s center and shape the larger gas reservoir that regulates star formation and fate of galaxies. We use optical data from the DESI survey and radio  observations from the LOFAR Two meter Sky Survey (LoTss).

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Credit: Image courtesy of Hailey Nelson/ Arizona State University.






Galaxies are enormous and hold hundreds of billions of stars. These stars form from cold, dense gas. Indeed, every large galaxy, including the Milky Way, is wrapped in a huge envelope of gas called the circumgalactic medium, or CGM. This gas is a reservoir of raw material and stretches 10-20 times the size of the visible portion of the galaxy. This CGM gas eventually cools, moves inward into the galaxy, and clumps together to form stars. Thus, the CGM plays a key role in shaping stars, planets, and even life within a galaxy. But astronomers have long puzzled over why, given how much star-forming gas surrounds them, galaxies don't have even more stars. What is keeping the fuel from cooling down and forming those stars?

A new study led by astronomers Sanchayeeta Borthakur of Arizona State University (ASU) and Namrata Roy, now at the Raman Research Institute (RRI), found evidence that narrow jets of heated plasma, blasted out by the supermassive black holes at galaxies' centers, can affect the whole galaxy even beyond what we can see, and may shape its future. The jets may reach out and disrupt the gas that galaxies need to keep growing. Their research has been published in the Astrophysical Journal Letters.  

“This is a pathbreaking result that solves the long-standing mystery of how black holes influence galaxies, their stars, and life as we know it!” said Borthakur, Associate Professor in ASU’s School of Earth and Space Exploration. “This work opens a new direction to explore further the intricacies of the connection between the supermassive black holes trillions of miles from where we are to how we came to be here.”

Little in size, big in influence 

When a black hole actively feeds on gas, it can release enormous energy that heats the surrounding gas. Even though these black holes can be powerhouses of energy, they are quite small and are roughly about the size of our solar system. On the other hand, their host galaxies can hold about 100 billion such solar systems. 

“The surprising question is: how can something so small energetically impact something so enormous?” said Roy, assistant professor at RRI and former ASU Exploration Prize Postdoctoral Fellow. 

One way to envision it is to think of an ant leaving its impression hundreds or thousands of kilometers away. Scientists still do not fully understand how energy from these active black holes reaches such distances and changes along the way.

The team’s study provides evidence as to how this could occur. They focused on active black holes that emit strong jets, which are narrow streams of hot, fast-moving plasma shooting out far beyond a galaxy’s visible edge. They looked for a distinct imprint in the ionization state of the gaseous reservoir caused by these jets. The ionized gas, or the “glow” from hydrogen gas they were looking for in the CGM, is so faint that no single galaxy would show it clearly. Hence, the team combined observations of hundreds of galaxies with active jets, using data from the Dark Energy Spectroscopic Instrument (DESI) survey and radio jet measurements from the LOFAR Two-meter Sky Survey (LoTSS). They combined measurements coming from the direction of the jet axes and searched for a specific telltale sign of ionized hydrogen gas along the jet path, known as H-alpha. 

Roy, Borthkur and colleagues showed that when averaged over all directions around the galaxies, the signal was weak; however, along the radio jets, the H-alpha signal became clear and strong. This indicates that the gas does not glow uniformly everywhere but is particularly bright along the jet path. A simple analogy is that the jet acts less like a lamp shining in all directions, and more like a powerful beam that makes the gas glow where it passes through. 

These findings show that black-hole jets do not affect the gas surrounding galaxies equally in all directions; instead, they leave a distinct impression by causing the gas to shine and become ionized mainly along the radio jet's path. They also found that the jets have the biggest impact, and that the glow from ionized hydrogen is brightest in two places: close to the galaxy where the jet first hits the CGM, and much farther out near the CGM’s outer edge, where the jet releases most of its energy. This provides a clear signature of how jets can illuminate or disrupt the surrounding gas, even at great distances, all the way to the CGM. This mechanism helps shape the galaxy's environment, influence its growth and evolution - it determines whether the galaxy continues to form stars or becomes quiescent.

“What excites me most is the scale of the connection,” Roy said. “A black hole is incredibly small compared to a galaxy, but its impact can reach hundreds of thousands of light-years, far into the galaxy’s outer reaches. The jet carries the energy outward, and the gas lights up along its path.

”As a check, the team also examined a tracer of cooler gas via the absorption signature of magnesium. Unlike the directional glow in H-alpha, Magnesium was more widely distributed isotropically and did not show any connection to the jet direction. This implies that the cool gas component might already exist as a reservoir surrounding the galaxy uniformly on all sides. Yet the jet brightens, heats, and ionizes gas along its own path, lighting up a trail and causing it to glow in H-alpha.

Black holes determine a galaxy's fate. 

The findings offer some of the clearest evidence yet for how a black hole can affect galaxies far beyond its central region. By heating, stirring, and disturbing gas throughout the CGM, jets can prevent that gas from cooling down and falling inward to fuel new stars. This acts as a brake on the galaxy’s growth, changes its fate, and makes it much less active in star formation.

This means the black hole is not just “feeding” at the center of the galaxy, as some might think. It also reaches out and changes the galaxy’s environment, which can eventually change its fate.

Specific Directions: Look both ways on the path 

Past studies searched for the signal but couldn't detect it, making this directional discovery an exciting breakthrough. The signal only appears when we look along the jet direction. If the astronomers had thought the CGM was the same in every direction, the team would have missed this discovery. The jet ionizes hydrogen gas along its path, making it glow in H-alpha in a very specific direction.

This study shows the value of large optical and radio surveys like the Dark Energy Spectroscopic Instrument (DESI) survey and the LOFAR Two-meter Sky Survey (LoTss). By combining many weak signals, astronomers can now study the behavior of galaxies that would otherwise stay hidden. The study also gives astronomers and theorists a new way to test how black-hole jets affect galaxies.

Contributing co-authors include Timothy Heckman at Johns Hopkins University and Tanmay Singh at Arizona State University. 

This work is supported by NASA, STScI, and NSF.