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Astronomers know that galaxies grow over time through mergers with other galaxies. We can see it happening in our galaxy. The Milky Way is slowly absorbing the Large and Small Magellanic Clouds and the Sagittarius Dwarf Spheroidal Galaxy.

For the first time, astronomers have found evidence of an ancient mass migration of stars into another galaxy. They spotted over 7,000 stars in Andromeda (M31), our nearest neighbor, that merged into the galaxy about two billion years ago.

purple haze surrounding a bright andromeda in the night sky over a horizon on Earth
The massive halo of gas is outlined in this image captured of the Andromeda galaxy. (NASA, ESA, and E. Wheatley (STScI))
The growth and evolution of galaxies is a hot topic in astronomy and one of the reasons the James Webb Space Telescope is grabbing a lot of headlines lately. One of the JWST's main scientific objectives is to look back in time to the Universe's earliest galaxies to understand how they've grown and evolved into what they are today. But it's not the only telescope that can shed light on the issue.

"Galaxies like M31 and our Milky Way are constructed from the building blocks of many smaller galaxies over cosmic history."

Arjun Dey, NOIRLab

These new observations of Andromeda and the inward migration of stars comes from the Dark Energy Spectroscopic Instrument (DESI.) It was built to measure the effect dark energy has on the expansion of the Universe. It does that by gathering optical spectra on tens of millions of objects, mostly galaxies and quasars, and then constructing a 3D map of the results.

DESI is similar to the more well-known Gaia spacecraft. Gaia has an ambitious goal to precisely map the positions and motions of billions of stars in the Milky Way. Gaia data led to a wealth of discoveries about our own galaxy. But it's confined to mapping stars in the Milky Way.

Now, thanks to DESI, astronomers have at least a partial map of the stars in Andromeda for the first time. And that map, including the motions of nearly 7,500 stars in the inner halo of the Andromeda Galaxy, is revealing their history.

These results are in a new paper titled "DESI Observations of the Andromeda Galaxy: Revealing the Immigration History of our Nearest Neighbor." It will appear in The Astrophysical Journal, and the lead author is Arjun Dey, an astronomer at the National Science Foundation's NOIRLab, the facility responsible for DESI.

DESI shows that about two billion years ago, another galaxy merged with Andromeda. The positions and motions of about 7,500 stars DESI measured reveal that they came from another galaxy. Theory told us this was how Andromeda and other galaxies grew so massive, but now there's a growing body of clear evidence.

"Our new observations of the Milky Way's nearest large galactic neighbor, the Andromeda Galaxy, reveal evidence of a galactic immigration event in exquisite detail," explained lead author Dey. "Although the night sky may seem unchanging, the Universe is a dynamic place. Galaxies like M31 and our Milky Way are constructed from the building blocks of many smaller galaxies over cosmic history."

The Milky Way experienced a similar merger between 8 to 10 billion years ago. Most of the stars in our galaxy's halo originated in a different galaxy and joined the Milky Way as a result of the ancient merger. Astronomers can learn more about the Milky Way's ancient history by closely observing this similar, more recent merger event in Andromeda.

"We have never before seen this so clearly in the motions of stars, nor had we seen some of the structures that result from this merger," said Sergey Koposov, an astrophysicist at the University of Edinburgh and coauthor of the paper. "Our emerging picture is that the history of the Andromeda Galaxy is similar to that of our own Galaxy, the Milky Way. The inner halos of both galaxies are dominated by a single immigration event."

For the first time, we get a glimpse of the structures that formed as a result of the merger. "The expected observational signatures of galactic migration include debris streams, shells, rings, and plumes, the expected outcomes of merger interactions between large galaxies and their companions," the authors write in their paper.

graph showing distribution of colours representing velocities of stars and their relative positions
Stars in Andromeda's inner halo and their velocities. (Dey et al., ApJ, 2023)
"We find clear kinematic evidence for shell structures in the Giant Stellar Stream, the Northeast Shelf and Western Shelf regions," the paper states. "The kinematics are remarkably similar to the predictions of dynamical models constructed to explain the spatial morphology of the inner halo. The results are consistent with the interpretation that much of the substructure in the inner halo of M31 is produced by a single galactic immigration event 1–2 Gyr ago."

"While hints of coherent structures have been previously detected in M31, this is the first time they have been seen with such detail and clarity in a galaxy beyond the Milky Way," the authors write in their paper. "The observations reveal intricate coherent kinematic structure in the positions and velocities of individual stars: streams, wedges, and chevrons."

graph showing colours representing velocities of stars and their distances from andromeda
Velocities vs. distance of some of Andromeda's stars by color. (Dey et al., ApJ, 2023)
Though the positions and velocities of the 7,500 stars play a major role in these findings, so did stellar metallicity. The team found high-metallicity stars in all of the sub-structures stemming from the merger. "We find significant numbers of metal-rich stars across all of the detected substructures, suggesting that the progenitor galaxy (or galaxies) had an extended star formation history, one perhaps more representative of more massive galaxies," the authors explain in their conclusion.

The study highlights similarities between Andromeda and Milky Way, strengthening the theoretical idea that mergers play a key role in galactic evolution and growth. "M31 is remarkably similar to the Milky Way in that the inner halos of both galaxies are dominated by stars from a single accretion event," the paper states. "Indeed, a recent study of the kinematics of Milky Way stars near the Sun reports chevron-shaped kinematic substructures that are reminiscent of those reported here."

DESI's power is on full display in this research. The results stem from DESI's ability to gather spectra from 5,000 objects simultaneously. This complex instrument is the most powerful multi-object survey spectrograph in the world and can reconfigure its 5,000 separate focal planes in only two minutes as it slews between targets.

"It's amazing that we can look out at the sky and read billions of years of another galaxy's history as written in the motions of its stars."

Joan R. Najita, NOIRLab.

It was designed to measure the spectra of over 40 billion distant galaxies and quasars to map the large-scale structure of the Universe and how dark energy fuels its expansion. Along the way, it's showing us how galaxies merge over time.

"This science could not have been done at any other facility in the world. DESI's amazing efficiency, throughput, and field of view make it the best system in the world to carry out a survey of the stars in the Andromeda Galaxy," said Dey. "In only a few hours of observing time, DESI was able to surpass more than a decade of spectroscopy with much larger telescopes."

"It's amazing that we can look out at the sky and read billions of years of another galaxy's history as written in the motions of its stars – each star tells part of the story," said co-author Joan R. Najita, also at NOIRLab. "Our initial observations exceeded our wildest expectations and we are now hoping to conduct a survey of the entire M31 halo with DESI. Who knows what new discoveries await!"

A trail found in the gas surrounding a distant galaxy could be the smoking gun pointing to a runaway supermassive black hole.

Based on an analysis of light that has traveled for more than 7.5 billion years to reach us, a team of astronomers has presented evidence of a colossal object ejected from its host galaxy 39 million years ago, which is now speeding across intergalactic space at 1,600 kilometers (994 miles) per second.

Although the black hole itself is invisible, its wake is not: shocks left in the tenuous intergalactic medium leave behind a trail of star formation in the compressed gas. The team's work shows one way we could identify quiescent supermassive black holes ejected from their galaxies to zoom, invisible and untethered, through intergalactic space.

The research, led by astrophysicist Pieter van Dokkum of Yale University, has been accepted into The Astrophysical Journal Letters and is available on preprint server arXiv.

The idea that a supermassive black hole could be ejected from its galaxy isn't actually that strange. In fact, astronomers have already identified what they think might be multiple supermassive black holes ejected from the centers of their galaxies (although none yet crossing into intergalactic space), and even one galaxy that appears to be missing its supermassive black hole altogether.

But those supermassive black holes all had one thing in common: they're active, which means they're surrounded by a cloud of material that's falling into their gaping mouths of doom. This process generates insane amounts of heat and light, which makes them much easier to spot.

But not all black holes are active. And those that are quietly minding their business between snacks, just hanging out doing their thing, emit no light we can detect and are therefore essentially invisible to our technology.

However, something as weighty as a supermassive black hole – millions to billions of times the mass of the Sun – might still leave behind tracks we can spot. This is what van Dokkum and his colleagues proposed: that the trail of an ejected supermassive black hole might be detected in the gas that surrounds a galaxy, known as the circumgalactic medium.

The discovery was made in the course of other investigations. The researchers were using Hubble to study a much closer dwarf galaxy called RCP 28. It was in that image that they discovered something that might just be the trail of a runaway supermassive black hole.

The image revealed a bright streak pointing straight at the center of an irregular galaxy. Initially, the researchers thought it was a cosmic ray, but it showed up in both the filters used to process the images. So, in October 2022, they took follow-up images using the Keck Observatory, to calculate the redshift of the galaxy and streak. This gave them a size: the streak measures over 200,000 light-years in length.

Analysis showed that the galaxy and the streak have the same redshift, meaning that they are likely associated with each other, and the streak and galaxy have the same color. The team had never seen anything like it.

Looking more closely, they found that the streak was not uniform in color or brightness. It also shows signs of strong ionization, and shock regions. Some of the ionization could be explained by the presence of very young, hot, massive stars; that's consistent with astrophysical shocks, which tend to compress gas and cause clumps of it to collapse under gravity, forming baby stars.

Streaks of light emerging from the centers of galaxies are not uncommon; these are usually astrophysical jets, powerful, narrow streams of plasma traveling at near light speeds, launched from the polar regions of active supermassive black holes. The streak the team found shows none of the hallmarks of an astrophysical jet, though.

It's possible, the team speculated, that the passage of a jet could have left a trail of star formation in its wake; but the streak in the images doesn't match any observed or simulated instance of jet-induced star formation on record.

In fact, the observed streak happens to be the very opposite of what astronomers would expect of a jet of gas; strongest at the farthest point from the galaxy, where there is less material, and narrower at greater distance, rather than spreading out like a jet.

The team believes that the best explanation is a runaway supermassive black hole, perturbing and compressing the circumgalactic medium as it travels through, leaving star formation behind.

You're probably wondering what can eject a supermassive black hole from its galaxy, and the answer is: another supermassive black hole. Or two. In the researchers' scenario, two galaxies merged once upon a time; the supermassive black holes at the cores of these galaxies came together into a binary supermassive black hole, and stayed that way for a while.

Then along came a third galaxy, and the supermassive black hole therein sank to the center of the newly merged trio of galaxies, resulting in a three-body interaction known as the Hills mechanism that flung one of the black holes away at high speeds.

diagram showing six images of merging galaxies, with three black holes forced to meet and orbit
Diagram (left) showing the in six steps a scenario in which three black holes (in red) could interact to produce the observed trail of stars. (van Dokkum et al., arXiv, 2023)
Future observations across multiple wavelengths will be able to help astronomers figure out if this is indeed the case. Meanwhile, because the feature is so distinctive, other examples should be relatively easy to find, particularly with more powerful instruments, like the upcoming infrared Nancy Roman Grace Space Telescope.

"We make the case that the feature is the wake of a runaway SMBH, relying on the small number of papers that have been written on this topic in the past fifty years," the researchers write in their paper.

"This area could benefit from further theoretical work, particularly since these papers propose a variety of formation mechanisms for the wakes. Hydrodynamical simulations that model the shocks and also take gravitational effects into account might bring these initial studies together in a self-consistent framework."

Bar charts and line graphs are both designed to help us visualize data. They are tools to convert numerical information into pictorial narratives that can be more easily comprehended. They don't change the data; they simply represent it.

They do represent it in different ways, however, and even those slight differences can be enough to bias us as we try to make predictions, according to a new study.

Researchers from the UK recruited more than 4,000 subjects over the internet, presented them with various graphs depicting past sales figures by a fictitious company, and asked them to predict future sales based on the trends so far.

Participants consistently made lower forecasts about how a trend in the data would develop when the data were presented in a bar chart, as opposed to the very same data being shown with either a line graph or unconnected points on a graph, the study found.

Graphs like these play key roles in society, points out lead author Stian Reimers, a behavioral scientist at City, University of London. As windows into complex data, visualizations help more people understand important issues – or at least that's the idea.

"In the past few years it seems like we have spent a lot of time looking at time series: whether it's the number of COVID-19 cases, electricity prices, or inflation rates, to try to work out what's coming next," Reimers says.

"What our research shows is that our predictions of what we think will happen next are affected not just by the trends we're looking at," he adds, "but the format in which they're displayed."

Reimers and co-author Nigel Harvey, a cognitive psychologist who studies judgment and decision making at University College London, recruited subjects using an internet rewards program, which incentivized participants to complete the two-minute online experiment and to make accurate predictions.

In the study's first two experiments, researchers gave the subjects a single graph – either a bar, line, or point graph – with 50 data points representing sales totals. Subjects could then click on the graph to record their prediction for the next 8 sales periods.

The first experiment featured a graph showing sales increases over time, which generally prompted subjects to predict continued success. The second experiment tried the opposite, with a graph showing decreases over time, and subjects responded with more pessimistic forecasts.

Across a variety of trends, subjects consistently made lower predictions about future sales when the same data were portrayed with a bar chart rather than a line or point graph.

The three formats used in the first part of the experiment. From left to right: a bar graph, a point format graph, and a line graph.
The three formats used in the experiment. From left to right: a bar graph, a point format graph, and a line graph. (Reimers & Harvey, International Journal of Forecasting, 2023)
In hopes of shedding light on why, the researchers tried adjusting the portrayal of the bars themselves. Maybe heavily shaded bars draw people's attention downward, biasing them just by associating the actual data points with the eye-catching shaded region below?

Yet subjects continued to lowball the bar graphs, the researchers found, even when the bars were left unshaded.

A final experiment proposed the bias might be reversible if bars emanate from the top of the graph rather than the bottom, but the findings were inconclusive, the researchers report.

The existence of this bias could cause problems in many ways, Reimers points out. It might lead people to misunderstand local COVID-19 or flu activity before visiting a vulnerable relative, for example, or to misjudge whether they can afford a mortgage.

Similar errors could have even wider ramifications in a business or public policy context, the researchers note, especially in situations where an individual "eyeballs" a graph to make rough estimates of what will happen next.

A bias like this could potentially be exploited to mislead people, although there are two sides to that coin. By understanding the bias and how it works, we might become better able to portray data accurately and help more of the general public understand it.

​​"A lot of the other biases that people show when trying to extrapolate trends are baked into the way we see the world and hard to change," Reimers explains.

"The format we use for our graphs is something we have complete control over, so it may be possible to use specific formats to help undo people's built-in biases and help people make more accurate judgments," he says.

The hottest startup in Silicon Valley right now is OpenAI, the Microsoft-backed developer of ChatGPT, a much-hyped chatbot that can write a poem, college essay, or even a line of software code.

Tesla tycoon Elon Musk was an early investor in OpenAI and Microsoft is reported to be in talks to up an initial investment of $1 billion to $10 billion in a goal to challenge Google's world-dominating search engine.

If agreed, the cash injection by the Windows-maker would value OpenAI at a whopping $29 billion, making it a rare tech-world success when major players such as Amazon, Meta, and Twitter are cutting costs and laying off staff.

"Microsoft is clearly being aggressive on this front and not going to be left behind on what could be a potential game-changing AI investment," said analyst Dan Ives of Wedbush Securities.

Before the release of ChatGPT, OpenAI had wowed tech geeks with Dall-E 2, software that creates digital images with a simple instruction.

Microsoft, which makes no secret of its AI ambitions, has integrated Dall-E 2 into several of its applications and now, according to a report in Bloomberg, the tech giant wants to graft ChatGPT to its Bing search engine to take on Google.

Since ChatGPT was introduced in November, the prowess of this chatbot has aroused the curiosity and fascination of internet users.

It is capable of formulating detailed and human-like answers on a wide range of subjects in a few seconds, raising fears that it is vulnerable to misuse by school cheats or for disinformation.

'Not cheap'
The dizzying success is due in part to OpenAI's clever marketing strategy in which it made its research accessible to non-experts, said AI specialist Robb Wilson, founder of OneReach.ai, a software company.

"Having this technology available to technologists was one thing. Offering it in a chat user interface and allowing non-developers to start playing with it ignited a conversation," he said.

Founded in late 2015, OpenAI is led by Sam Altman, a 37-year-old entrepreneur and former president of startup incubator Y Combinator.

The company has counted on the financial support of prestigious contributors from the start, including LinkedIn co-founder Reid Hoffman, investor Peter Thiel, and Musk.

The multi-billionaire served on OpenAI's board until 2018, but left to focus on Tesla, the electric vehicle company.

The startup also relies on a team of computer scientists and researchers led by Ilya Sutskever, a former Google executive who specializes in machine learning.

OpenAI, which did not respond to AFP's inquiries, had about 200 employees by 2021, according to a query made directly on ChatGPT.

For now, despite the excitement generated by ChatGPT, the company has yet to find a path to financial independence.

Founded as a nonprofit, the startup became a "capped for-profit" company in 2019 to attract more investors and this week co-founder Greg Brockman said that a paid version of ChatGPT was in the works.

The search for funding seems necessary for a company with exorbitant expenses.

In a Twitter exchange with Musk in early December, Altman acknowledged that each conversation on ChatGPT costs OpenAI several US cents.

According to estimates by Tom Goldstein, an associate professor in the University of Maryland's computer science department, the company is shelling out $100,000 a day for its bot, or about $3 million a month.

Partnering with Microsoft, which provides the startup with its remote computing services, could cut costs, but "either way, it's not cheap," Goldstein said.

"Some say it's wasteful to pour these kinds of resources… into a demo," he added.

While some dog breeds have unfortunate reputations for being more aggressive than others, veterinarians and other animal experts have long been skeptical about this.

A new study of 665 domestic dogs (Canis familiaris) in Brazil also points towards factors other than breed having stronger influences over this 'problematic' behavior.

"The results highlight something we've been studying for some time: behavior emerges from interaction between the animal and its context," explains University of São Paulo ethologist Briseida de Resende.

"The environment and the owner-pet relationship, as well as morphology, are all factors that influence how pets interact with us and how we interact with them."

Previous research defines canine aggression "as a dog's tendency to both act threateningly, with raised hackles and tail, bared teeth, heightened body posture, growling and to act aggressively, by attacking or biting".

Through a series of questionnaires for owners, University of São Paulo ethologist Flavio Ayrosa and colleagues found several strong associations.

The good news is that dogs with owners who play with them and take them for regular walks were likelier to be less aggressive towards owners and strangers. Training levels were a strong indicator too.

But the absence of aggression towards strangers was 73 percent more likely when the dog's owner was female. The s*x of the dog also appears to have a role, with a 40 percent lower likelihood of aggression towards owners from females rather than male dogs.

Some physical traits also showed associations, which may explain why many point their fingers at specific breeds. Dogs with unhealthily short snouts, known as brachycephalic breeds, were 79 percent more likely to display aggression towards their owners.

What's more, as height and weight decreased, undesirable behaviors, including non-social fear, attention-seeking behaviors, and hyperactivity, also increased, as seen in past studies.

But a combination of these different factors was the best predictor, rather than just a body characteristic or an environmental one alone.

"We found relationships, but it's impossible to say which comes first. In the case of the factor 'walking the dog', for example, it may be that people walked their dog less because the animal was aggressive, or the dog may have become aggressive because the owner didn't take it out enough," says Ayrosa.

"Traits such as weight, height, cranial morphology, s*x, and age influence the interaction between dogs and their environment. They may spend more time inside the home because of them, for example."

Regardless, it's important to remember that aggression is a natural form of communication for all animals, and like all behaviors, it is complex.

While no one wants their companion animals to rely on aggression as a first response when feeling worried, stressed, or threatened, sometimes there is a valid reason for instances of aggression that can be resolved, such as pain.

"Rather than determining aggression to a single factor common to the species or specific breeds, our results reinforce how individual behavior, combined with dogs' unique genetics, physiology, life experiences, and environmental contexts, interact throughout development to produce the observed expression patterns," the team concludes in their paper.

An analysis of the residue on ceramics found in an ancient embalming workshop has given us new insights into how ancient Egyptians mummified their dead.

Even more astonishingly, a team of scientists has been able to link different substances to the specific parts of the body on which they were used.

This discovery is, in part, thanks to the residues themselves, which were studied using biomolecular techniques; but many of the vessels were intact, including not just the names of their contents, but instructions for their use.

"We have known the names of many of these embalming ingredients since ancient Egyptian writings were deciphered," says archaeologist Susanne Beck of the University of Tübingen in Germany in a statement provided to the press.

"But until now, we could only guess at what substances were behind each name."

The workshop was part of an entire burial complex in Saqqara, Egypt, that was discovered by a joint German-Egyptian team in 2018, dating back to the 26th or Saite Dynasty, between 664–525 BCE.

The grave goods recovered were spectacular, including mummies, canopic jars containing their organs, and ushabti figurines, to serve the dead in their afterlife.

Alabaster canopic jars recovered from Saite-Saqqara. (Egyptian Ministry of Antiquities)
And there was the workshop, filled with ceramic jars, measuring cups, and bowls, neatly labeled according to their contents or use.

Led by archaeologist Maxime Rageot of the University of Tübingen, the researchers conducted a thorough examination of 31 of these vessels, using gas chromatography-mass spectrometry to determine the ingredients of the embalming materials therein.

The detailed results are fascinating, and in some cases, completely unexpected.

"The substance labeled by the ancient Egyptians as antiu has long been translated as myrrh or frankincense. But we have now been able to show that it is actually a mixture of widely differing ingredients," Rageot explains in the statement.

These ingredients were cedar oil, juniper or cypress oil, and animal fat, the team found, although the mixture may vary from place to place and time to time.

The team also compared instructions inscribed on some of the vessels to their contents to determine how each mixture was used. Instructions included "to put on his head", "bandage or embalm with it", and "to make his odor pleasant".

Eight different vessels had instructions regarding the treatment of the deceased's head; pistachio resin and castor oil were two ingredients that only appeared in these vessels, often in a mixture that contained other elements, such as elemi resin, plant oil, beeswax, and tree oils.

Some of the vessels found in the embalming workshop. (Saqqara Saite Tombs Project, University of Tübingen; M. Abdelghaffar)
Animal fat and Burseraceae resin were used to deal with the smell of the decomposing body, and animal fat and beeswax were used to treat the skin on the third day of treatment. Tree oils or tars, along with plant oil or animal fat, could be used to treat the bandages used to wrap the mummy, as found in eight more vessels.

Even more fascinating is what these mixtures can reveal about global trade at the time.

Pistachio, cedar oil, and bitumen were probably all sourced from the Levant on the Eastern shore of the Mediterranean.

However, elemi and another resin called dammar come from much farther away: Elemi grows in both sub-Saharan Africa and Southeast Asia, but the tree that produces dammar only grows in Southeast Asia.

Therefore, it's possible that these two resins traveled the same trade route to Egypt, the researchers note in their paper, suggesting that a great deal of effort went into sourcing the specific ingredients used for embalming. This possibly played a significant role in the establishment of global trade networks.

Meanwhile, the team's work on the 121 bowls and cups recovered from the workshop will continue.

"Thanks to all the inscriptions on the vessels, we will in future be able to further decipher the vocabulary of ancient Egyptian chemistry that we did not sufficiently understand to date," says archaeologist Philipp Stockhammer of Ludwig Maximilian University of Munich in Germany in the statement.

The excavation of the tomb complex was led by archaeologist Ramadan Hussein of the University of Tübingen, who sadly passed away last year, before the work could be completed.