theconversation.com – Fan Zou, Graduate Student in Astronomy and Astrophysics, Penn State – 2024-07-12 07:33:14
Most of the blue points in this sky survey image are accreting supermassive black holes emitting strong X-rays. Fan Zou (Penn State) and the XMM-SERVS Collaboration
Black holes are remarkable astronomical objects with gravity so strong that nothing, not even light, can escape them. The most gigantic ones, known as “supermassive” black holes, can weigh millions to billions times the mass of the Sun.
So, how do these supermassive black holes become super massive? To answer this question, our teamof astrophysicists looked back in time across the universe’s 13.8 billion-year history to track how supermassive black holes have grown from the early days to today.
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We constructed a model of the overall growth history of supermassive black holes spanning the past 12 billion years.
How do supermassive black holes grow?
Supermassive black holes grow primarily in two ways. They can consume gas from their host galaxies in a process called accretion, and they can also merge with each other when two galaxies collide.
An artist’s illustration of an accreting supermassive black hole. The central black hole is black, while its surrounding gas heats up and shines to produce light. Nahks Tr’Ehnl (Penn State)
When supermassive black holes consume gas, they almost always emit strong X-rays, a type of high-energy light invisible to the naked eye. You’ve probably heard of X-rays at the dentist, where they are sometimes used to examine your teeth. The X-rays used by astronomers generally have lower energies than medical X-rays.
So how can any light, even invisible X-rays, escape from black holes? Strictly speaking, the light is not coming from the black holes themselves, but from the gas just outside them. When gas gets pulled toward a black hole, it heats up and shines to produce light, like X-rays. The more gas a supermassive black hole consumes, the more X-rays it will produce.
Thanks to the data accumulated over more than 20 years from three of the most powerful X-ray facilities ever launched into space – Chandra, XMM-Newton and eROSITA – astronomers can capture X-rays from a large number of accreting supermassive black holes in the universe.
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This data allows our research team to estimate how fast supermassive black holes grow by consuming gas. On average, a supermassive black hole can consume enough gas to amount to about the mass of the Sun each year, with the exact value depending upon various factors.
For example, the data shows that a black hole’s growth rate, averaged over millions of years, is strongly connected to the mass of all the stars in its host galaxy.
How often do supermassive black holes merge?
Besides feeding on gas, supermassive black holes can also grow by merging with each other to form a single, more massive black hole when galaxies collide.
Supercomputer cosmological simulations can predict about how often these events happen. These simulations aim to model how the universe grows and evolves over time. The countless galaxies flying through space are kind of like bricks, building up the universe.
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These simulations show that galaxies and the supermassive black holes they host can undergo multiple mergers across the span of cosmic history.
Our team has tracked these two growth channels – gas consumption and mergers – using X-rays and supercomputer simulations, and then combined them to construct this overall growth history, which maps the growth of black holes across the universe over billions of years.
Our growth history revealed that supermassive black holes grew much faster billions of years ago, when the universe was younger.
Back in the early days, the universe contained more gas for supermassive black holes to consume, and supermassive black holes kept emerging. As the universe aged, the gas was gradually depleted, and supermassive black hole growth slowed. About 8 billion years ago, the number of supermassive black holes stabilized. It hasn’t increased substantially since then.
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An illustration of a merger of two supermassive black holes. Scott Noble (NASA GSFC)
When there isn’t enough gas available for supermassive black holes to grow by accretion, the only way for them to get larger is through mergers. We didn’t see very many cases of that in our growth history. On average, the most massive black holes can accumulate mass from mergers at a rate up to the mass of the Sun every several decades.
Looking forward
This research has helped us understand how over 90% of the mass in black holes has accumulated over the past 12 billion years.
However, we still need to investigate how they grew in the very early universe to explain the remaining few percentages of the mass in black holes. The astronomical community is starting to make progress exploring these early supermassive black holes, and we hope to find more answers soon.
Children with difficult temperaments, including personality tendencies such as irritability and having a hard time being comforted, are only slightly more likely than other children to have insecure attachment relationships with one or both of their parents, according to our research. This finding refutes the long-standing notion held by many psychologists that early attachment behaviors are mainly determined by a child’s temperament.
An attachment relationship reflects the child’s expectations about their caregiver in times of need. A secure attachment is likely if a caregiver is consistently available and emotionally supportive when the child is alarmed. However, if a child learns that their caregiver will not be there when needed or will not effectively soothe them, chances are they will develop an insecure attachment relationship with that caregiver.
Part of that is understanding what influences the way child-parent attachments form. Even infants show stark differences in temperament, and some psychologists have argued that these individual dispositions may also explain how youngsters interact with caregivers. Even the most sensitive and loving parent could feel challenged when caring for a difficult child – does that dynamic influence the quality of their attachment relationship?
How we do our work
With 29 other researchers, we started a research consortium to study the quality of children’s attachment relationships with their mothers and fathers – or what we call their attachment networks.
For this meta-analysis, we combined data collected over the past 40 years on 872 children from North American families.
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Researchers observed these kids interacting separately with their mothers and fathers and completed assessments designed to evaluate children’s attachment behaviors: How do they seek comfort in times of need? How easily do they find reassurance in their parents? How do they explore their environment in the presence of their parents?
In addition, parents reported on the degree of their children’s difficult temperament. How likely was the child to experience intense negative emotions, such as anger, sadness or fearfulness?
It seemed logical that children who have a more difficult temperament might tend to have more insecure attachment relationships within the family – but that’s not exactly what we found. Instead, a difficult temperament had very little to do with the number of insecure attachment relationships a child had with their parents.
Greater tendencies toward a difficult temperament had just a very small impact – less than 1%, according to our statistical analysis – on children’s likelihood to have multiple insecure attachment relationships. And temperament was only slightly more difficult in infants who had insecure attachment with both parents rather than with only one or neither of the parents.
The results from our latest study suggest that even children with inborn characteristics of a difficult temperament can benefit from the advantages that come from multiple secure attachments. These findings may reassure worried parents.
What still isn’t known
Further research is needed to explain the small increase in insecure attachments we did identify for kids with difficult temperaments.
For example, children’s difficult temperament increases the likelihood of negative parenting, including anger and coercing and overcontrolling behaviors. These in turn can intensify children’s negative emotions. Over time, it’s possible this two-way street of negative reactions increases the probability of insecure attachment relationships between child and parents.
Interventions that promote positive parenting and sensitive discipline increase children’s attachment security with their parents. So, parents can foster secure attachment with deliberate efforts to be more sensitive to the child’s emotional needs.
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One thing has become clear. The secure attachment relationships that play a critical role in cognitive and emotional development are not closed off to children born with difficult temperaments.
The Research Brief is a short take on interesting academic work.
Tensions between China, Taiwan and the U.S. aren’t limited to aerial military maneuvers and drills on the high seas. The shadow conflict is also playing out in the technological arena.
One of the central drivers of the deepening geopolitical rifts between China on one side and Taiwan and the U.S. on the other is dominance over global semiconductor supply chains. This is because semiconductors – or microchips – power everything from smartphones and home office software to critical infrastructure and advanced military hardware.
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As international demand for sophisticated microchips surges, not least owing to the blistering growth of artificial intelligence, so does their strategic value to the global economy and the progress of individual nations. China today spends as much importing microchips as it does importing oil.
Taiwan did not emerge as the world’s semiconductor powerhouse by accident. The self-governing island has been producing high-quality microchips for decades due in large part to its flexible production network and world-class engineering talent pool.
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Yet Taiwan faces a delicate balancing act in maintaining its market superiority in semiconductors, especially when it comes to exporting advanced technologies to China. For one, Taiwanese policymakers are understandably determined to both avoid political entanglements with a country that views the island as its own territory and hold on to the island’s intellectual property. Moreover, Taiwan wants to keep microchips from powering Chinese missiles currently pointed at the capital, Taipei.
The road to regulating chips
Until the early 1990s, the transfer of technologies to China was prohibited under Taiwanese law. But regulations were weakly enforced. As a result, Taiwanese businesses frequently circumvented existing sanctions by rerouting investments through then-British Hong Kong. The reality was that the chip industry was a lucrative source of revenue for the island.
Taiwan’s approach to regulating the flow of technologies started to change in 1993 when President Lee Teng-hui implemented the “no haste, be patient” policy. The strict ban was relaxed and replaced by a system in which additional layers of oversight were added to highly advanced technologies, deals valued at more than US$50 million and specialized critical infrastructure projects.
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Crafted over decades, this “outbound investment screening” system features multiple checks intended to safeguard Taiwan’s core chip technologies. Taiwanese authorities are actively involved in monitoring and overseeing investment decisions involving China made by the island’s semiconductor companies. Officials are also keen to ensure that local chipmakers are aligned with Taiwan’s strategic interests, while minimizing political ties with its neighbor.
During the screening process, Taiwanese companies are required to submit detailed investment plans to government-appointed reviewers for approval. For example, when a Taiwanese semiconductor firm, such as the world’s largest chip manufacturer TSMC, considers establishing a new facility in China, it must first undertake a rigorous approval process.
Changing calculations
While the cautious policy shift appears prescient today given rising geopolitical tensions, at the time it was considered out of step with the direction of more open global trade relations with China. The restrictive human rights considerations that had curbed Western trade with China were eased in the 1990s after intensive lobbying by U.S. corporations. In 2000, U.S. President Bill Clinton granted China permanent normal trade relations, paving the way for its accession to the World Trade Organization a year later. Trade with China, including of advanced technologies, exploded thereafter.
A visitor explores the TSMC exhibition at the World Semiconductor Congress 2022 in Nanjing, Jiangsu province, China. CFOTO/Future Publishing via Getty Images
But Washington’s strategic calculations over trade with China have shifted dramatically over the past decade. In 2018, the U.S. singled out China as a strategic competitor, designating several Chinese hackers and the government itself as national security threats. By August 2023, President Joe Bidendirected the Treasury Department to draft regulations to develop an outbound investment security program to safeguard semiconductor, quantum and AI technologies.
A few months later, the U.S. issued sweeping restrictions on the trade of advanced chips and chipmaking equipment with China. In early 2024, the European Union released a white paper proposing to do the same.
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Of course, Taiwan has its own specific political concerns when it comes to China. Given Beijing’s long-standing ambition to, as Chinese leaders put it, “reunify” Taiwan with the mainland, local officials are particularly aware how doing business with China might have unpredictable and damaging political ramifications.
The Taiwanese National Security Bureau has long warned that Beijing is using business to covertly advance its political ambition, including by leveraging Taiwanese capital to build influence and proxies within Taiwan. And in late 2023, Taiwan’s National Science and Technology Council announced a list of over 20 core technologies it wanted to prevent Beijing from acquiring, including know-how and raw material to make chips smaller than 14 nanometers.
New challenges for Taiwan’s regulations
Taiwanese authorities and businesses have built on the outbound screening system in order to push back against Chinese influence. In recent years, additional principles to protect Taiwan’s semiconductor dominance have been introduced, including requiring Taiwanese investors to retain a controlling interest in all Chinese subsidiaries.
Nonetheless, Taiwan’s outbound investment screening system is facing multiple tests. While it is designed to curb the transfer of advanced Taiwanese technologies to China, it also has to oversee financial investments from Taiwan into China’s surging chipmaking sector.
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In 2022, for example, the Taiwanese technology group Foxconn announced an investment in Tsinghua Unigroup through its Chinese subsidiary. Tsinghua Unigroup is backed by China’s National Integrated Circuit Industry Investment Fund and controlled by a Beijing-based private equity firm. Owing to Foxconn’s failure to submit a required preapproval application to the outbound investment screening authorities, the Taiwanese government imposed a fine on the company, which eventually withdrew its investment.
Inside the Taiwan Semiconductor Research Institute in Hsinchu, Taiwan. Annabelle Chih/Getty Images
China’s growing chip industry is also expanding its local supply chain, raising questions about whether Taiwan should expand restrictions on other suppliers linked to semiconductor manufacturers. After the U.S. introduced export controls on China in late 2023, the Chinese firm Huawei aggressively expanded its chip production network by leveraging its affiliates and Taiwanese suppliers. Four Taiwanese semiconductor firms that had previously been approved for outbound investment were subsequently accused of aiding Huawei in building China’s domestic chip supply chain.
Confronting China’s ambition
With access to Taiwanese semiconductors increasingly restricted, China has aggressively pursued greater technological autonomy. It has done so by reducing its reliance on imports of advanced equipment and materials from U.S., Japan, the Netherlands and Taiwan.
There are legitimate concerns in the West that tightening international export restrictions on microchips and relevant suppliers could inadvertently strengthen China’s determination to accelerate the development of its domestic semiconductor production.
Official data appears to corroborate this view; China’s overall imports of microchips in 2023 were below 2017 levels. Exports of Taiwanese chips to China dropped by 18% in 2023.
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Meanwhile, China’s National Bureau of Statistics reported that overall domestic chip production grew by 40% in the first quarter of 2024. Its share of global capacity to produce logic chips at 10-22 nanometers could rise from 6% to 19% by 2032.
But these data points do not necessarily mean that China is close to technological autonomy. Most of the increases in domestic chip production involve “mature” chips for household appliances and electric vehicles, rather than the most advanced chips required to accelerate AI computing power.
Meanwhile, China is still dependent on Taiwan for its semiconductors. The decrease in overall chip imports could be a result of international export restrictions on the most cutting-edge semiconductors needed for high-end smartphones and other AI-driven, high-performance computing products.
Coordinating international efforts
Restricting China’s access to the global superconductor supply chain is challenging. While doing so makes China reliant on Taiwanese chips – and as such may serve as a temporary protective shield against invasion – it could also exacerbate Beijing’s insecurities, pushing President Xi Jinping to hasten efforts to become technologically self-sufficient in advanced chips manufacturing. At the same time, outright bans on these chips hasn’t prevented China from producing a range of semiconductors using foreign capital and technology.
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To address this challenge, Taiwan’s screening mechanisms not only need to remain nimble and vigilant – they need to be supported by a coordinated international approach. Only then will it be possible to slow the progress of authoritarian regimes in the AI race.
The seventh season of Julia Child’s “The French Chef,” the first of the television series to air in color, revealed how color can change the experience of food. While Child had charmed audiences in black and white, seeing “Bouillabaisse à la Marseillaise” in color helped elevate the experience from merely entertaining to mouthwatering.
I am a psychologist who studies visual abilities. My work, through a serendipitous research journey into individual differences in food recognition, uncovered a unique role for color in emotional responses to food.
This journey started when my students and I measured how people vary in their ability to recognize images of prepared food. Over the past 20 years, we and other researchers have learned that people vary more than originally suspected in how well they discriminate and identify objects, like birds, cars or even faces.
It seems obvious that some people know more than others about birds or cars. Yet, interestingly, there is as much variation in face recognition ability, even though virtually every sighted person has experience seeing faces.
Experience with food is also universal. We were curious how much people would vary in their ability to recognize food items. Our tests simply ask people to match images of the same dish among similar ones, or to find the oddball dish among others. People vary a great deal on these tasks, and some of this variation is explained by a general ability to recognize objects of any kind.
But a portion of the food recognition differences among people was not explained by this general ability. Instead, we speculated that this variability may be related to people’s attitude toward new foods. People who strongly endorse statements like “I don’t trust new foods” or “I am very particular about the foods I eat” have what’s called food neophobia. It can lead to poor diet quality, resulting in nutritional deficiencies and higher risk of chronic disease.
Example of a test trial to measure food recognition ability: Which of these foods is the oddball? Top row shows the dishes in color, while the bottom row simulates the most common form of color blindness (based on daltonlens.org). The second image is the oddball: Notice how the pizza crust is more obvious with normal color. Rouzes/E+, Carlo A/Moment, Yulia Naumenko/Moment, rudisill/E+ via Getty Images
Color connects food neophobia to recognition
While we were publishing our results, other scientists were debating new findings about how the brain reacts to food and color. Different research groups had identified brain areas in the visual system that responded preferentially to images of food. For instance, looking at a bowl of pasta would activate these brain areas, but not looking at a pile of string.
The scientific disagreement was about what it meant to identify a selectivity for food in areas of the brain already known for their responsiveness to color.
Was it possible that color was not critical to food recognition, while still playing a special role? We decided to replicate our initial study, with images of food in gray scale.
The results could have been predicted by Child herself: Without color, people unsurprisingly made a few more errors and mistook different dishes as the same kind of food, but the pattern of variation across people was otherwise unchanged. Those with a higher general visual ability did better with food, and we again found a specific ability for food that goes beyond this general effect.
Based on these results, we proposed two separate components of food-specific recognition ability. One is independent of color and explains why the results are the same in the experiments with and without color. The other one, related to emotional responses, is based on color and evidenced by the finding that food neophobia is only related to food recognition when the food appears in color.
We then made an entirely new prediction: Would people with color blindness – men, really, because color blindness affects 16 times more men than women – be less food neophobic than those with normal color perception? Because someone who is colorblind experiences food in a restricted range of color, some of the signals that raise flags about freshness, safety or otherwise drive anxiety about novel food could be limited.
We recruited participants online, including men in our study based on how they answered one question about color blindness that was buried in a long screening questionnaire. Our participants had no idea that we were interested in color blindness when we asked them then to fill out the Food Neophobia Scale that measures how resistant people are to new foods.
The role of color in emotional responses to food opens up new avenues for addressing extreme cases of food neophobia. As researchers learn more about the intricate relationship between color perception and food, we might develop targeted interventions to improve dietary habits. Just like Julia Child’s colorful dishes, understanding and leveraging the power of color could enhance the appreciation and enjoyment of food.