Extremely rare star found from ancient universe

Astronomers find extremely rare star in its original galaxy 

The gorgeous snap, taken by the Dark Energy Camera (DECam) mounted atop the Víctor M. Blanco 4-meter (13 feet) Telescope in Chile, gives a glistening field of stars inside the dwarf galaxy Pictor II. Discoveries like this are cosmic archaeology, uncovering rare stellar fossils that preserve the fingerprints of the universe’s first stars. The ancient and rare star PicII-503 is helping astronomers understand how carbon became so abundant in the universe. A glistening field of stars against a black background is more than 10 billion years old. 

What it is: Star PicII-503 inside the Pictor II dwarf galaxy

Where it is: 150,000 light-years from Earth in the Pictor constellation

But it isn't just a pretty picture. Nestled inside this is the star PicII-503, a stellar furnace so ancient that it's classed as a Population II, or second-generation, star, making it among the oldest stars in the universe. Scientists have adopted the role of "cosmic archaeologists" to discover a rare, iron-deficient second-generation star, essentially a fossil record of our universe's chemical evolution. Just as uncovering artifacts here on Earth teaches us about lost generations of humans, this observation provides hard evidence of how the first generation of stars died to chemically enrich their successors. The second generation, or POP II, star was discovered in the dwarf galaxy Pictor II, located around 150,000 light-years from Earth in the constellation Pictor, using the Dark Energy Camera (DECam) mounted atop Víctor M. Blanco 4-meter Telescope. Designated PicII-503, the star has only 1/40,000th of the iron contained within the sun, which is a third-generation, or (somewhat confusingly) POP I, star. The fact that PicII-503 has the lowest concentration of iron ever seen beyond the Milky Way makes it one of the most primordial stars ever discovered.

Population II stars formed when the cosmos was young and stars had yet to fuse heavier elements into existence, meaning they are composed primarily of hydrogen and helium. This means that PicII-503 has roughly only 1-40,000th of the iron contained within our much younger sun. This deficit isn't the most extraordinary about PicII-503, however. The team also found that this POP II star has a massive overabundance of carbon, with its ratio of carbon-to-iron over 1,500 times greater than the same ratio in the sun. This overabundance mirrors the unique carbon signature of low-iron stars found in the nebulous outer halo of the Milky Way. "Discoveries like this are cosmic archaeology, uncovering rare stellar fossils that preserve the fingerprints of the universe’s first stars," Chris Davis, National Science Foundation Program Director for NOIRLab said. The first confirmed example of a POP II star found in a faint dwarf galaxy, PicII-503 was highlighted as an extremely metal-poor star in data collected by DECam's MAGIC (Mapping the Ancient Galaxy in CaHK) survey. This 54-night observing endeavor was developed with the explicit purpose of identifying the oldest and most chemically primitive stars in the Milky Way and its dwarf galaxy companions.

But what the star lacks in iron it makes up for in carbon. Like many Pop II stars, PicII-503 is unusually rich in the stuff, having a carbon-to-iron ratio that's more than 1,500 times the ratio in the sun. The first stars in the universe, or POP III stars, were born when the chemical abundance of the cosmos didn't extend beyond hydrogen, helium and a smattering of heavier elements, which astronomers collectively call "metals. "This meant that these POP III stars were also dominated by hydrogen with just a little helium and very little in terms of metals. These stars forged the first carbon and iron in their cores, material which was distributed into the interstellar medium when these stars went supernova and exploded at the end of their lives. Interstellar clouds of gas and dust enriched with these metals eventually cooled and collapsed to birth the second generation of stars, stars which were more metal-rich thanks to the donation of heavy elements from their predecessors. This makes POP II akin to time capsules, recording an important stage in the chemical enrichment of the universe. "Discovering a star that unambiguously preserves the heavy metals from the first stars was at the edge of what we thought possible, given the extreme rarity of these objects," team leader Anirudh Chiti of Stanford University said. "With the lowest iron abundance ever derived in any ultra-faint dwarf galaxy, PicII-503 provides a window into initial element production within a primordial system that is unprecedented."

Astronomers have proposed many theories why this may be the case but because many Pop II stars are spotted after they've migrated away from their birthplaces, these suggestions have been hard to verify. "Without data from MAGIC, it would have been impossible to isolate this star among the hundreds of other stars in the vicinity of the Pictor II ultra-faint dwarf galaxy," Chiti said. Chiti and colleagues combined MAGIC data with observations from the Very Large Telescope (VLT) in the Atacama Desert region of northern Chile and the Baade Magellan Telescope to discover low iron and calcium abundances of PicII-503, the lowest seen beyond our home galaxy. In turn, this revealed that PicII-503 was the first record of chemical enrichment found in a dwarf galaxy. One possible explanation for the shockingly low iron-to-carbon ratio of PicII-503 is that when POP III stars went supernova, these explosions were relatively low in energy. This would have meant that while lighter elements like carbon were blasted into the interstellar medium, heavy elements like iron fell back into the wreckage of the supernova.

But PicII-503 is still located within its primordial dwarf galaxy, so astronomers acted as "stellar archeologists," using the star’s composition to test their theories. The star’s carbon-rich makeup lends credence to an idea that, during the violent supernova explosion at the end of a star’s life, lightweight carbon in the star’s outer shell is flung farther away than other elements. The fact that PicII-503 is found in one of the smallest dwarf galaxies ever seen, with a correspondingly low gravitational influence, supports the idea of POP III stars dying in low-energy supernovas. "What excites me the most is that we have observed an outcome of the very initial element production in a primordial galaxy, which is a fundamental observation!” Chiti said. "It also cleanly connects to the signature that we have seen in the lowest-metallicity Milky Way halo stars, tying together their origins and the first-star-enriched nature of these objects." This could also explain why carbon ends up everywhere in the universe, making it an extremely suitable element to act as the key building block for life here on earth.

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Ground water and it's shortages

 Groundwater depletion : The most critical scientific and political challenge   

 

As the world’s largest perennial and distributed freshwater resource, groundwater will play a central role in one of the most critical scientific and political challenges of this century: improving human access to fresh water for the production of food and safe drinking water while sustaining key ecosystems in a warming world. Groundwater is critical to irrigated agriculture and domestic water access. Unfortunately, unsustainable pumping is depleting groundwater reserves at rapid and accelerating rates, especially in cultivated dry lands. This groundwater depletion poses a challenge to global urbanization and may represent the world’s greatest threat to irrigated agriculture. Depletion trends can be reversed by human interventions, but the interventions which have refilled depleted aquifers have not been compiled and compared. For half the world's population, the water in their drinking glasses comes from below them. Groundwater also supplies 40% of global irrigation projects. Alarmingly, more than a third of the planet's aquifers, or groundwater basins, are dropping. Declining water tables leave entire regions vulnerable to drought, land subsidence or seawater intrusion while damaging ecosystems and reducing water access. Properly securing this resource is a matter of social, humanitarian and environmental security.

Fortunately, there have been some success stories. UC Santa Barbara professor Scott Jasechko dove into the details of 67 cases of aquifer recovery in a study. He found that most successful initiatives incorporated multiple intervention categories, and over 80% involved sourcing an alternative water supply. It provides many insights on the strategies which communities and resource managers can use to address declining groundwater resources. "The cases in this review are a reminder that groundwater depletion is not inevitable," said Jasechko, a professor at the Bren School of Environmental Science & Management. "They highlight how humans have solved this problem in different places around the globe." For example, By selecting several interventions from a menu of strategies, Beijing was able to reverse their declining groundwater. Groundwater is being depleted, often at rapid and unsustainable rates, in regions across the globe as agricultural, domestic, and industrial demands continue to grow. Is such groundwater loss inevitable? Jasechko reviews an array of examples that demonstrate that it is not and that well-designed human intervention can slow, stop, or even reverse depletion trends. Knowing which methods are effective in countering groundwater depletion could facilitate additional efforts to fight it, thereby mitigating land surface subsidence, water table deepening, reductions in crop yields, and seawater contamination of coastal aquifers.

In 2024, Jasechko and his colleagues compiled the largest assessment of groundwater levels around the world, spanning nearly 1,700 aquifers. They presented a picture of dwindling resources and accelerating declines. But it also offered a few instructive examples of where things were going well, which served as the basis for the current study. Jasechko pored over these success stories, arranging interventions into categories which he could then sort and compare. Three broad recovery strategies emerged: finding alternative water sources, implementing policies and environmental markets, and artificially replenishing aquifers. Aquifers are like groundwater bank accounts replenished by deposits from rain, snowmelt and surface infiltration. Right now, there are a lot of dangerously low balances. We can address these by changing our lifestyle and consumption; in other words, enacting policies and creating infrastructure to reduce the demand on groundwater. We can also get a side hustle. Alternative water sources can offset groundwater demand or even be deposited back into our account through aquifer recharge. The current paper has a lot of nuanced comparisons and discussions since each case study has a unique combination of factors. However, several trends appeared. Two-thirds of the cases involved interventions from multiple categories. "I think this emphasizes the value of multi-pronged strategies to address groundwater level declines," Jasechko said. The moral here is don't put all your eggs in one basket. Or in this case, don't carry all your water in one bucket. Meanwhile, 81% included an alternative water source that helped offset groundwater demands. Jasechko suspects part of this strategy's appeal is that it requires the least behavioral change. "If another water source is available, accessing it can help meet water demands and offset the need to pump groundwater," he said. "This can sidestep more challenging conversations about reducing total water use, but accessing alternative supplies can have its own drawbacks." Specifically, this solution is often expensive and can end up displacing the issue to another location. In contrast, policy changes benefit from low overhead and energy costs. They also most directly target the behaviors that led to drawdown in the first place. However, they often have major impacts on local economies that have relied on groundwater use for a long time. Groundwater recharge can obviate the need to reduce pumping, "which can be a viable strategy for communities that have built their economies around groundwater use," Jasechko remarked. But, again, the water needs to come from somewhere, and getting it into the aquifer requires energy.

Interventions which have reversed groundwater depletion trends include changes to policies, use of alternative water supplies and the artificial replenishment of aquifers. Jasechko acknowledges that this is not a comprehensive analysis, or even a correlative study. It only considers places previously studied by other scientists and resource managers. "It likely overrepresents places where groundwater science has been published in English-language academic journals," he said. It also doesn't start with actions and follows them to their effects. "We need a database of all the places where comparable interventions were implemented, and the groundwater levels before and after," Jasechko said. This is actually a goal that his longtime collaborator, UCSB professor Debra Perrone, is working toward. This all means there's no guarantee that the solutions detailed here will work at other places. At the very least, they will need to be adapted to local conditions. But Jasechko still sees value in outlining the success stories. "This study can help create a menu of options for managers and stakeholders to consider as they develop locally relevant strategies to try to make things better," he said. These examples and analysis, he believes, can provide the activation energy to begin addressing this problem more widely. "Groundwater depletion is widespread globally. These cases highlight that there are ways to turn things around," Jasechko said. "Globally, there are many more bad news cases than good news cases. Yet, I am somewhat encouraged by the clever ways that certain managers and stakeholders have addressed the problem of groundwater depletion in specific places, because they show that the menu of strategies is longer than I originally anticipated."

Refilling depleted aquifers can have cobenefits such as halting land subsidence, slowing seawater intrusion, reducing drought vulnerability, restoring ecosystems and improving water access. However, new challenges can emerge when groundwater rises to very shallow depths, such as waterlogged soils, destabilized buildings, increased liquefaction risks and intensified flood hazards. Together, groundwater recovery cases highlight the benefits of intervening to stop groundwater depletion while also cautioning against overcorrections that risk overfilling aquifers. Scientifically, greater pan‑disciplinary study of interventions designed to halt groundwater declines can help identify transferable tactics to address groundwater depletion. Strategically, stakeholders and managers can consider borrowing and implementing components of the strategies reviewed, which have proven to be successful in one or more cases, thereby enabling successful strategies of the past to empower ongoing efforts to combat groundwater depletion. Beijing provides a great illustration of how combining different strategies can tackle even a megacity's water woes. Between 1950 and 2000, groundwater pumping around Beijing had caused the water table to plummet by more than 20 meters in some places. In 2003, the government started construction of canals and pumping stations, and by 2015 it was delivering water to the city and surrounding areas from wetter regions farther to the south. At the same time, the city began using more reclaimed water in the 21st century, with much of this allocated to environmental uses like watering trees and grasslands as well as replenishing lakes and rivers. Furthermore, the authorities banned pumping from the region's deep confined aquifers for industrial uses after the water deliveries began. Both the area's shallow and deep aquifer has begun to recover, and land subsidence rates have slowed down in and around Beijing. Springs which had previously dried up have begun flowing once again. Meanwhile, the region's irrigated agriculture remains highly productive and its sustainability is no longer jeopardized by falling groundwater levels.

Recent work has highlighted that groundwater depletion is not an inevitability and interventions can slow, stop and even reverse depletion trends. This work profiles dozens of cases of groundwater recovery, where groundwater levels rose after a prolonged period of decline. These cases span a wide range of climate and land-use conditions and highlight how groundwater recovery can take place in both urban and rural areas and in both wet and dry climates. The interventions which drive groundwater recovery span three general categories. First, most groundwater recovery cases involve access to an alternative water source to offset groundwater demands. These alternative water sources usually involve diversions of rivers, highlighting the critical importance of coordinating surface-water and groundwater management. Because such diversions reduce river discharges, some groundwater recovery episodes have exacerbated water scarcity elsewhere. Second, about half of the cases involve changes to policies or market conditions which reduced groundwater demands, such as the implementation and enforcement of groundwater withdrawal fees or restrictions on pumping. Third, many cases of groundwater recovery involve artificial groundwater recharge. This artificial recharge can be deliberate (e.g., diverting river water into intentionally leaky ponds) or incidental (e.g., leaky irrigation canals). Altogether, many cases of groundwater recovery involve coincident implementation of multiple interventions, demonstrating the merits of multipronged strategies to reverse groundwater declines. "However, just because groundwater is recovering at any given moment in time doesn't mean that the work is done," Jasechko warns. In 1957, Green Bay, Wisconsin constructed a 43-km pipeline to augment their groundwater supply with water from Lake Michigan. This helped restore their stressed aquifer for a while, before additional demand sent it falling again for decades. In 2006, the city built another, 100 km-long  pipeline to bring in more water from the Great Lakes, which has brought their aquifer back on the path to recovery. "It's important to keep monitoring after an initial phase of groundwater recovery so that managers can adapt to changing conditions," Jasechko said.

Groundwater depletion poses a challenge to irrigated agriculture and water access. Depleted aquifers can be refilled, but the interventions which have successfully refilled depleted aquifers are rarely reviewed. This work reviews cases of groundwater recovery, where groundwater levels rose after a prolonged period of decline. The interventions which spurred groundwater recovery included policy changes, artificial groundwater recharge and increased reliance on another water source instead of groundwater. Groundwater recovery can improve water access, restore ecosystems, slow seawater intrusion and halt land subsidence. However, excessive groundwater recovery can waterlog soils, destabilize buildings, increase liquefaction risks and intensify flood hazards. Stakeholders and managers may consider adapting aspects of these interventions to address groundwater depletion elsewhere. At the moment, Jasechko is investigating why recovery speed and distribution can vary so widely across different basins. And these case studies will help develop better predictions of how quickly groundwater levels may recover under different interventions. "An important question is: What scope and scale of intervention is required for depleted aquifers to start recovering?" he said. These are important questions for communities and resource managers who would like to improve the situation, but just don't have a sense as to what magnitude of intervention is required. Jasechko summarized his findings in following key themes:-

Most success stories involved multiple kinds of interventions.

The majority included accessing alternative water sources.

Interventions that reduced pumping often helped aquifers recover.

Good policies still require sound implementation and enforcement.

Sometimes recovery can happen over just a few years.

When recovery is slow, gradual policy phase-in can be helpful.

Recovery can vary widely within a given area.

Improvements aren't permanent, and can easily reverse.

It's important to manage groundwater quality alongside quantity.

Interventions should consider the direct and indirect impacts of climate change.

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