̽��ֱ�� of Cambridge - ̽��ֱ�� of Arizona

Neon sign identified by JWST gives clue to planet formation

Anonymous — Tue, 05 Mar 2024 15:06:11 +0000

Planetary systems like our Solar System seem to contain more rocky objects than gas-rich ones. Around our sun, these include the inner planets, the asteroid belt and the Kuiper belt. But scientists have known for a long time that planet-forming discs start with 100 times more mass in gas than in solids, which leads to a pressing question; when and how does most of the gas leave the disc/system?

JWST is helping scientists uncover how planets form, by advancing understanding of their birthplaces, the circumstellar discs surrounding young stars. In a new study published in the Astronomical Journal, a team of scientists including those from the ̽��ֱ�� of Leicester, the ̽��ֱ�� of Cambridge and led by the ̽��ֱ�� of Arizona, image for the first time an old planet-forming disc (still very young relative to the Sun) which is actively dispersing its gas content.

Knowing when the gas disperses is important as it constrains the time that is left for nascent planets to consume the gas from their surroundings.

During the very early stages of planetary system formation, planets coalesce in a spinning disc of gas and tiny dust around the young star. These particles clump together, building up into bigger and bigger chunks called planetesimals. Over time, these planetesimals collide and stick together, eventually forming planets. ̽��ֱ��type, size, and location of planets that form depend on the amount of material available and how long it remains in the disc. So, the outcome of planet formation depends on the evolution and dispersal of the disc.

At the heart of this discovery is the observation of T Cha, a young star (relative to the Sun) enveloped by an eroding disc notable for its vast dust gap, approximately 30 astronomical units in radius. For the first time, astronomers have imaged the dispersing gas (aka winds) using the four lines of the noble gases neon (Ne) and argon (Ar), one of which is the first detection in a planet-forming disc. ̽��ֱ��images of [Ne II] show that the wind is coming from an extended region of the disc. ̽��ֱ��team is also interested in knowing how this process takes place, so they can better understand the history and impact on our solar system.

Scientists have been trying to understand the mechanisms behind the winds in protoplanetary discs for over a decade. ̽��ֱ��observations by JWST represent a huge step-change in the data they have to work with, compared to previous data from ground-based telescopes.

“We first used neon to study planet-forming discs more than a decade ago, testing our computational simulations against data from Spitzer, and new observations we obtained with the ESO VLT,” said co-author Professor Richard Alexander from the ̽��ֱ�� of Leicester. “We learned a lot, but those observations didn’t allow us to measure how much mass the discs were losing.

“ ̽��ֱ��new JWST data are spectacular, and being able to resolve disc winds in images is something I never thought would be possible. With more observations like this still to come, JWST will enable us to understand young planetary systems as never before.”

“These winds could be driven either by high-energy stellar photons (the star's light) or by the magnetic field that weaves the planet-forming disc,” said Naman Bajaj from the ̽��ֱ�� of Arizona, the study’s lead author.

To differentiate between the two, the same group, this time led by Dr Andrew Sellek of Leiden Observatory and previously of the Institute of Astronomy at the ̽��ֱ�� of Cambridge, performed simulations of the dispersal driven by stellar photons. They compare these simulations to the actual observations and find dispersal by high-energy stellar photons can explain the observations, and hence cannot be excluded as a possibility.

“ ̽��ֱ��simultaneous measurement of all four lines by JWST proved crucial to pinning down the properties of the wind and helped us to demonstrate that significant amounts of gas are being dispersed,” said Sellek.

To put it into context, the researchers calculate that the mass dispersing every year is equivalent to that of the moon! These results will be published in a companion paper, currently under review at the Astronomical Journal.

̽��ֱ��[Ne II] line was discovered towards several planet-forming discs in 2007 with the Spitzer Space Telescope and soon identified as a tracer of winds by team member Professor Ilaria Pascucci at the ̽��ֱ�� of Arizona; this transformed research efforts focused on understanding disc gas dispersal. Now the discovery of spatially resolved [Ne II] - as well as the first detection of [Ar III] - using the James Webb Space Telescope, could become the next step towards transforming our understanding of this process.

̽��ֱ��implications of these findings offer new insights into the complex interactions that lead to the dispersal of the gas and dust critical for planet formation. By understanding the mechanisms behind disc dispersal, scientists can better predict the timelines and environments conducive to the birth of planets. ̽��ֱ��team's work demonstrates the power of JWST and sets a new path for exploring planet formation dynamics and the evolution of circumstellar discs.

Reference:
Naman S Bajaj et al. ‘JWST MIRI MRS Observations of T Cha: Discovery of a Spatially Resolved Disk Wind.’ ̽��ֱ��Astronomical Journal (2024). DOI: 10.3849/1538-3881/ad22e1

Adapted from a ̽��ֱ�� of Leicester press release.

̽��ֱ��winds that help to form planets in the gaseous discs of early solar systems have been imaged for the first time by the James Webb Space Telescope (JWST) using the noble gases neon and argon.

ESO/M. Kornmesser

Artist's impression of the surroundings of the supermassive black hole in NGC 3783

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Research reveals accidental making of ‘Patient Zero’ myth during 1980s AIDS crisis

fpjl2 — Wed, 26 Oct 2016 17:02:10 +0000

A new study proves that a flight attendant who became notorious as the human epicentre of the US AIDS crisis of the 1980s – and the first person to be labeled the ‘Patient Zero’ of any epidemic – was simply one of many thousands infected in the years before HIV was recognised.

Research by a historian from the ̽��ֱ�� of Cambridge and the genetic testing of decades-old blood samples by a team of US scientists has demonstrated that Gaétan Dugas, a French-Canadian gay man posthumously blamed by the media for spreading HIV across North America, was not the epidemic’s ‘Patient Zero’.

In fact, work by Dr Richard McKay, a Wellcome Trust Research Fellow from Cambridge’s Department of History and Philosophy of Science, reveals how the very term ‘Patient Zero’ – still used today in press coverage of outbreaks from Ebola to swine flu to describe the first known case – was created inadvertently in the earliest years of investigating AIDS.

Before he died, Dugas provided investigators with a significant amount of personal information to assist with studies into whether AIDS was caused by a sexually transmitted agent. McKay’s research suggests that this, combined with confusion between a letter and a number, contributed to the invention of ‘Patient Zero’ and the global defamation of Dugas.

Dr McKay’s work has added important contextual information to the latest study, led by Dr Michael Worobey from the ̽��ֱ�� of Arizona and published today in the journal Nature, which has compared a new analysis of Dugas’s blood with eight other archived serum samples dating back to the late 1970s.

“Gaétan Dugas is one of the most demonised patients in history, and one of a long line of individuals and groups vilified in the belief that they somehow fuelled epidemics with malicious intent,” says McKay.

While his wider research traces this impulse to blame back several centuries, for the Nature paper McKay located the immediate roots of the term “Patient Zero” in an early ‘cluster study’ of US AIDS patients.

Mistaken for zero

Reports emerged in early 1982 of historical sexual links between several gay men with AIDS in Los Angeles, and investigators from the Centers for Disease Control (CDC) undertook a study to interview these men for the names of their sexual contacts.

They uncovered more links across southern California, but one connection was named several times despite not residing in the state: Case 057, a widely travelled airline employee. Investigators found that his sexual contacts included men in New York City, and some of his sexual partners developed symptoms of AIDS after he did.

CDC investigators employed a coding system to identify the study’s patients, numbering each city’s cases linked to the cluster in the sequence their symptoms appeared (LA 1, LA 2, NY 1, NY 2, etc.). However, within the CDC, Case 057 became known as ‘Out(side)-of-California’ – his new nickname abbreviated with the letter ‘O.’

Because other cases were numbered, it was here that the accidental coining of a new term took place. “Some researchers discussing the investigation began interpreting the ambiguous oval as a digit, and referring to Patient O as Patient 0,” says McKay. “‘Zero’ is a capacious word. It can mean nothing. But it can also mean the absolute beginning.”

̽��ֱ��LA study expanded, due in no small part to information provided by Case 057. Over 65% of men in the cluster reported more than 1,000 partners in their lifetimes, over 75% more than 50 in the past year. But most could offer only a handful of names of those partners.

As well as donating plasma for analysis, Case 057 managed to provide 72 names of the roughly 750 partners he’d had in the previous three years. Also, his distinctive name may have been easier for other men to remember, says McKay. “ ̽��ֱ��fact that Dugas provided the most names, and had a more memorable name himself, likely contributed to his perceived centrality in this sexual network.”

By the time the expanded study was published in 1984, the same year Dugas died of his illness, the cluster showed dozens of cases connecting several North American cities. Near the very centre of an accompanying diagram is a floating case that links both coasts, the itinerant Dugas. Case 057, the ‘Out-of-California’ case, had been rechristened simply as “Patient 0” – causing much speculation in the media.

‘Casting’ an epidemic

̽��ֱ��journalist Randy Shilts would use the LA cluster study as an important thread in his bestselling book on the AIDS crisis, And the Band Played On. During the book’s research, he became fascinated by the study’s ‘Patient 0’.

Motivated to find out more about this man, Shilts eventually learned his name in 1986. ̽��ֱ��journalist tracked down his friends and colleagues for interviews, and, as “Patient Zero,” made him one of the more memorable villains in his book.

To call attention to the crisis, Shilts set out to “humanise the disease”, says McKay, who discovered that an early outline for the book actually listed ‘ ̽��ֱ��Epidemic’ itself among the cast of characters. “To Shilts, Dugas as Patient Zero came to represent the disease itself.”

̽��ֱ��1982 study had initially suggested to investigators that the period between infection and the appearance of AIDS symptoms might be several months.

By the time Shilts’s book was published in 1987, however, it was known that an infected individual might not display symptoms for several years, and that the study was unlikely to have revealed a network of infection. Yet Shilts uncritically resurrected the story of the Los Angeles cluster study and its ‘Patient 0,’ with long-standing consequences.

̽��ֱ��journalist’s decision provoked immediate criticism from AIDS activists in lesbian and gay communities across North America and the UK. Some of their works of protest are cited in the Nature study, and explored in greater detail in McKay’s own forthcoming book and in a 2014 article he published in the Bulletin of the History of Medicine.

“In many ways, the historical evidence has been pointing to the fallacy of Patient Zero for decades,” explains McKay. “We now have additional phylogenetic evidence that helps to consolidate this position.”

McKay describes the very phrase ‘Patient Zero’ as “infectious.” “Long before the AIDS epidemic there was interest in locating the earliest known cases of disease outbreaks. Yet the phrases ‘first case,’ ‘primary case,’ and ‘index case’ didn’t carry the same punch.

“With the CDC’s accidental coining of this term, and Shilts’s well-honed storytelling instincts, you can see the consolidation of an ‘infectious’ formula that would become central to the way many would make sense of later epidemics.”

Blaming ‘others’

Now, almost 30 years since Shilts’s book, analysis of the HIV-1 genome taken from Dugas’s 1983 blood sample, contextualised through McKay’s historical research, has shown that he was not even a base case for HIV strains at the time, and that a trail of error and hype led to his condemnation as the so-called Patient Zero.

̽��ֱ��researchers say it may be naïve to expect Patient Zero’s legendary status, or the popular impulse to attribute blame for disease outbreaks, to ever disappear.

“Blaming ‘others’ – whether the foreign, the poor, or the wicked – has often served to establish a notional safe distance between the majority and groups or individuals identified as threats,” says McKay.

“In many ways, the US AIDS crisis was no different – as the vilification of Patient Zero shows. It is important to remember that, in the 1970s, as now, the epidemic was driven by individuals going about their lives unaware they were contracting, and sometimes transmitting, a deadly infection.

“We hope this research will give researchers, journalists and the public pause before using the term Patient Zero. ̽��ֱ��phrase carries many meanings and a freighted history, and has seldom pointed to what its users have intended.”

A combination of historical and genetic research reveals the error and hype that led to the coining of the term ‘Patient Zero’ and the blaming of one man for the spread of HIV across North America.

We hope this research will give researchers, journalists and the public pause before using the term Patient Zero

Richard McKay

Harry Reasoner introduces the 60 Minutes program featuring ‘Patient Zero’ and the American AIDS crisis, broadcast on CBS in November 1987.

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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