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Star formation near the Sun is driven by expansion of the Local Bubble – Nature.com

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Abstract

For decades we have known that the Sun lies within the Local Bubble, a cavity of low-density, high-temperature plasma surrounded by a shell of cold, neutral gas and dust1,2,3. However, the precise shape and extent of this shell4,5, the impetus and timescale for its formation6,7, and its relationship to nearby star formation8 have remained uncertain, largely due to low-resolution models of the local interstellar medium. Here we report an analysis of the three-dimensional positions, shapes and motions of dense gas and young stars within 200 pc of the Sun, using new spatial9,10,11 and dynamical constraints12. We find that nearly all of the star-forming complexes in the solar vicinity lie on the surface of the Local Bubble and that their young stars show outward expansion mainly perpendicular to the bubble’s surface. Tracebacks of these young stars’ motions support a picture in which the origin of the Local Bubble was a burst of stellar birth and then death (supernovae) taking place near the bubble’s centre beginning approximately 14 Myr ago. The expansion of the Local Bubble created by the supernovae swept up the ambient interstellar medium into an extended shell that has now fragmented and collapsed into the most prominent nearby molecular clouds, in turn providing robust observational support for the theory of supernova-driven star formation.

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Fig. 1: A 3D spatial view of the solar neighbourhood.
Fig. 2: The evolution of the Local Bubble and sequential star formation at the surface of its expanding shell.

Data availability

The datasets generated and/or analysed during the current study are publicly available on the Harvard Dataverse (https://dataverse.harvard.edu/dataverse/local_bubble_star_formation/), including Extended Data Table 1 (https://doi.org/10.7910/DVN/ZU97QD), Extended Data Table 2 (https://doi.org/10.7910/DVN/1VT8BC), per-star data for individual stellar cluster members (https://doi.org/10.7910/DVN/1UPMDX) and the cluster tracebacks (https://doi.org/10.7910/DVN/E8PQOD).

Code availability

The results generated in this work are based on publicly available software packages and do not involve the extensive use of custom code. Given each star’s reported Gaia data, we use the astropy38 package to obtain the Heliocentric Galactic Cartesian positions and velocities. The extreme deconvolution algorithm in the astroML51 package is used to estimate the mean 3D positions and velocities of the stellar clusters. The Orbit functionality in the galpy40 package is used to perform the dynamical tracebacks. The dynesty43 package is used to fit the analytic superbubble expansion model and determine the best-fit parameters governing the Local Bubble’s evolution.

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Acknowledgements

The visualization, exploration and interpretation of data presented in this work were made possible using the glue visualization software, supported under NSF grant numbers OAC-1739657 and CDS&E:AAG-1908419. The interactive figures were made possible by the plot.ly python library. D.P.F. acknowledges support by NSF grant AST-1614941 ‘Exploring the Galaxy: 3-Dimensional Structure and Stellar Streams’. D.P.F., A.A.G. and C.Z. acknowledge support by NASA ADAP grant 80NSSC21K0634 ‘Knitting Together the Milky Way: An Integrated Model of the Galaxy’s Stars, Gas, and Dust’. A.B. acknowledges support by the Excellence Cluster ORIGINS, which is funded by the German Research Foundation (DFG) under Germany’s Excellence Strategy -EXC-2094-390783311. J.A. acknowledges support from the Data Science Research Centre and the TURIS Research Platform of the University of Vienna. J.G. acknowledges funding by the Austrian Research Promotion Agency (FFG) under project number 873708. C.Z. acknowledges that support for this work was provided by NASA through the NASA Hubble Fellowship grant number HST-HF2-51498.001 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. C.Z., A.A.G., J.A. and S.B. acknowledge Interstellar Institute’s program ‘The Grand Cascade’ and the Paris-Saclay University’s Institut Pascal for hosting discussions that encouraged the development of the ideas behind this work.

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Contributions

C.Z. led the work and wrote the majority of the text. All authors contributed to the text. C.Z., A.A.G. and J.A. led interpretation of the observational results, aided by S.B., M.F. and A.B. who helped interpret their significance in light of theoretical models for supernova-driven star formation. C.Z. and A.A.G. led the visualization efforts. J.S.S. and D.P.F. helped shape the statistical modelling of the Local Bubble’s expansion. C.Z., A.A.G. and J.S.S. contributed to the software used in this work. J.G. and C.S. provided data for and the subsequent interpretation of the 3D kinematics of the Orion region. D.K. helped to develop the code used to model the 3D positions and motions of stellar clusters described in the Methods.

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Catherine Zucker.

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Extended data figures and tables

Extended Data Fig. 1 1D and 2D marginal distributions (“corner plot”) of the model parameters governing the evolution of the Local Bubble’s expanding shell.

Parameters include the time since the first explosion (i.e. the age of the Local Bubble), texp, the density of the ambient medium the bubble is expanding into, n0, the time between supernova explosions powering its growth, 𝞓tSNe, and the thickness/uncertainty on the expanding shell radius 𝞓R. In the 1D distributions, the vertical dashed lines denote the median and 1𝝈 errors, while in the 2D distributions, we show the 0.5𝝈, 1𝝈, 1.5𝝈, and 2𝝈 contours.

Extended Data Fig. 2 Temporal evolution of the Local Bubble, based on the fit to the dynamical tracebacks and the analytic expansion model22 summarized in the Methods section.

Panel a) The evolution of the Local Bubble’s expansion velocity vexp. Panel b) The evolution of the Local Bubble’s shell radius Rshell. Panel c) The evolution of the average momentum injection per supernova . The thick purple line represents the median fit, while the thin purple lines represent random samples. We estimate a current radius of (165pm 6) pc and current expansion velocity of (6,.7,_-0.4^+0.5) km/s, corresponding to time t=0 Myr (the present day).

Extended Data Fig. 3 PDF of the estimate of the number of supernovae required to power the Local Bubble’s expansion.

The estimate is obtained by comparing the shell’s present-day momentum to the average momentum injected by supernovae.

Extended Data Fig. 4 Analysis of the stellar tracebacks of the UCL and LCC clusters, whose progenitors were likely responsible for the supernovae that created the Local Bubble.

The scatter points indicate the positions of the current cluster members of UCL and LCC, which are colored as a function of time (spanning the present day in pink to 30 Myr ago in black). Panel a: Using Hipparcos data and adopting a solar peculiar motion (U, V, W) = (10.0, 5.2, 7.2) km/s46, previous literature6,7 find that UCL and LCC were born outside the Local Bubble (black trace4) 15 Myr ago and only entered its present-day boundary in the past 5 Myr (reproduced from Fig. 6 in ref. 6). Panel b: We attempt to reproduce the results from previous literature6,7 using the same data and solar motion, but are unable to account for the curvature of the tracebacks, finding the UCL and LCC formed just inside its northern boundary 15 Myr ago. Panel c: Using a different value for the solar motion, (U, V, W) = (10.0, 15.4, 7.8) km/s41 but the same Hipparcos data, we find that UCL and LCC were born near the center of the Local Bubble. Panel d: Finally, using updated Gaia data but the same adopted solar motion used in panel c. (U, V, W) = (10.0, 15.4, 7.8) km/s41, we also find that UCL and LCC were born near the center of the bubble, given an updated model for its surface13.

Extended Data Table 1 Summary of the 3D positions and 3D velocities of young stellar clusters within 400 pc of the Sun
Extended Data Table 2 Temporal evolution of cluster births at the surface of the Local Bubble’s expanding shell

Supplementary information

Peer Review File

Supplementary Figure 1

Interactive 3D visualization of dense gas and young stars on the Local Bubble’s surface. This figure is the interactive 3D counterpart to Fig. 1. The figure supports interactive panning, zooming and rotation. Individual data layers can be toggled on/off by clicking on the layer in the legend on the right-hand side of the figure. The surface of the Local Bubble13 is shown in purple. The short squiggly coloured lines (or ‘skeletons’) demarcate the 3D spatial morphology of dense gas in prominent nearby molecular clouds11. The 3D cones indicate the positions of young stellar clusters, with the apex of the cone pointing in the direction of stellar motion. The Sun is marked with a yellow cross. We also overlay the morphology of the 3D dust (grey blobby shapes9) and the models for two Galactic scale features—the Radcliffe Wave (red)16 and the Split (blue)10. The Per-Tau Superbubble15 (green sphere) is also overlaid.

Supplementary Figure 2

Interactive 3D visualization of the Local Bubble’s expansion. This figure is the interactive 3D counterpart to Fig. 2. The figure supports interactive panning, zooming and rotation. Individual data layers can be toggled on/off by clicking on the layer in the legend on the right-hand side of the figure. Stellar cluster tracebacks are shown with the coloured paths. Before the cluster birth, the tracebacks are shown as semi-transparent circles meant to guide the eye, since our modelling is insensitive to the dynamics of the gas before its conversion into stars. After the cluster birth, the tracebacks are shown with filled circles and terminate in a large dot, which marks the cluster’s current position. For time snapshots ≤14 Myr ago, we overlay a model for the evolution of the Local Bubble (purple sphere), as derived in the Methods. Click ‘Play Forward’ to see the Local Bubble evolve starting 17 Myr ago and progressing forwards to the present day. Click ‘Play Backward’ to see the evolution in reverse. Click ‘Pause’ to stop the animation. Alternatively, drag the time slider back and forth to view the Local Bubble’s expansion at any time. To jump to epochs of particular interest, click on any of the ‘action’ buttons (for example, ‘UCL Born’) on the right-hand side of the figure.

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Zucker, C., Goodman, A.A., Alves, J. et al. Star formation near the Sun is driven by expansion of the Local Bubble.
Nature (2022). https://doi.org/10.1038/s41586-021-04286-5

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  • Received: 18 August 2021

  • Accepted: 26 November 2021

  • Published: 12 January 2022

  • DOI: https://doi.org/10.1038/s41586-021-04286-5

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Scientists study trajectory of meteorite that landed in B.C. in October – Red Deer Advocate

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VANCOUVER — Scientistsstudying a meteorite that landed next to a British Columbia woman’s head last year say it was diverted to that path about 470 million years ago.

The small meteorite broke through a woman’s ceiling in Golden, B.C., in October, landing on her pillow, next to where she had been sleeping moments earlier.

Philip McCausland,a lead researcher mapping the meteorite’s journey, said Monday they know the 4.5-billion-year-old rock collided with something about 470 million years ago, breaking into fragments and changing the trajectory of some of the pieces.

McCausland, who’s an adjunct professor at Western University in London, Ont., said the meteorite is of scientific significance because it will allow scientists to study how material from the asteroid belt arrives on Earth.

“There’s 50,000 to 60,000 identified meteorites now in the world, but most have no context. We don’t know really where they came from,” he said.

“In cases where we have known orbits, where they were observed coming in well enough that we can reconstruct what the orbit was before it hit the Earth’s atmosphere, we can actually (determine) where they came from in the asteroid belt. Golden is one of those,” he said, referring to the location of where the meteorite landed.

Researchers determined the meteorite is an L chondrite, one of the most commonly found types of meteorites to fall to Earth. Despite this, he said only about five L chondrites have known orbits.

He said the Canadian team is now working with scientists in Switzerland, the U.K., U.S. and Italy to learn more about the meteorite and its path to Golden.

“We know we’re still going to get something interesting out of this,” McCausland said. “We actually do want to get a good handle on how things get delivered from the asteroid belt, and this is a useful part of putting that together.”

Most of the meteorite has been returned to Ruth Hamilton, the woman who had the close call, and McCausland said it’s up to her to decide what to do with it.

Whether she decides to keep, sell or donate the rock, he said there is cultural significance of the rock to Canada. If she sells it to an international buyer, she would be required to go through the exportation process, he said.

Hamilton said she hasn’t yet made up her mind on what to do with the meteor. It’s currently sitting in a safety deposit box.

“I don’t have any plans for it right now, but once they’re done analyzing it, I’ll get all the documentation that proves it’s a meteorite,” she said. “It’s going to be officially named the Golden Meteorite.”

Before her roof is permanently repaired this spring, Hamilton said she intends to remove the section where the meteorite crashed through to keep it preserved alongside the rock.

McCausland said the research will likely conclude in May, and the scientists will then publish their work in an academic journal.

“Whenever something like this happens, I like to tell people it could happen to any of us; anyone can find a meteorite. It’s unlikely one will crash through your roof, but it can happen,” McCausland said. “It’s nature and, if anything, it’s a reminder that we’re part of something bigger.”

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Elon Musk’s Starlink Is Causing More Streaks to Appear in Space Images – Gizmodo

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A Starlink satellite streak appears in a ZTF image of the Andromeda galaxy, as pictured on May 19, 2021.
Image: ZTF/Caltech

Researchers at the Zwicky Transient Facility in California have analyzed the degree to which SpaceX’s Starlink satellite constellation is affecting ground-based astronomical observations. The results are mixed.

The new paper, published in The Astrophysical Journal Letters and led by former Caltech postdoctoral scholar Przemek Mróz, offers some good news and some bad news. The good news is that Starlink is not currently causing problems for scientists at the Zwicky Transient Facility (ZTF), which operates out of Caltech’s Palomar Observatory near San Diego. ZTF, using both optical and infrared wavelengths, scans the entire night sky once every two days in an effort to detect sudden changes in space, such as previously unseen asteroids and comets, stars that suddenly go dim, or colliding neutron stars.

But that doesn’t mean Starlink satellites, which provide broadband internet from low Earth orbit, aren’t having an impact. The newly completed study, which reviewed archival data from November 2019 to September 2021, found 5,301 satellite streaks directly attributable to Starlink. Not surprisingly, “the number of affected images is increasing with time as SpaceX deploys more satellites,” but, so far, science operations at ZTF “have not yet been severely affected by satellite streaks, despite the increase in their number observed during the analyzed period,” the astronomers write in their study.

The bad news has to do with the future situation and how satellite megaconstellations, whether Starlink or some other fleet, will affect astronomical observations in the years to come, particularly observations made during the twilight hours. Indeed, images most affected by Starlink were those taken at dawn or dusk. In 2019, this meant satellite streaks in less than 0.5% of all twilight images, but by August 2019 this had escalated to 18%. Starlink satellites orbit at a low altitude of around 324 miles (550 km), causing them to reflect more sunlight during sunset and sunrise, which creates a problem for observatories at twilight.

Astronomers perform observations at dawn and dusk when searching for near-Earth asteroids that might appear next to the Sun from our perspective. Two years ago, ZTF astronomers used this technique to detect 2020 AV2—the first asteroid entirely within the orbit of Venus. A concern expressed in the new paper is that, when Starlink gets to 10,000 satellites—which SpaceX expects to achieve by 2027—all ZTF images taken during twilight will contain at least one satellite streak. Following yesterday’s launch of a Falcon 9 rocket, the Starlink megaconstellation consists of over 2,000 satellites.

In a Caltech press release, Mróz, now at the University of Warsaw in Poland, said he doesn’t “expect Starlink satellites to affect non-twilight images, but if the satellite constellation of other companies goes into higher orbits, this could cause problems for non-twilight observations.” A pending satellite constellation managed by OneWeb, a UK-based telecommunications firm, will orbit at an operational altitude of 745 miles (1,200 km), for example.

Launch of a SpaceX Falcon 9 rocket with 49 Starlink satellites on board, as imaged on January 18, 2022.
Launch of a SpaceX Falcon 9 rocket with 49 Starlink satellites on board, as imaged on January 18, 2022.
Photo: SpaceX

The researchers also estimated the fraction of pixels that are lost as a result of a single satellite streak, finding it to be “not large.” By “not large” they mean 0.1% of all pixels in a single ZTF image.

That said, “simply counting pixels affected by satellite streaks does not capture the entirety of the problem, for example resources that are required to identify satellite streaks and mask them out or the chance of missing a first detection of an object,” the scientists write. Indeed, as Thomas Prince, an astronomer at Caltech and a co-author of the study pointed out in the press release, a “small chance” exists that “we would miss an asteroid or another event hidden behind a satellite streak, but compared to the impact of weather, such as a cloudy sky, these are rather small effects for ZTF.”

SpaceX has not responded to our request for comment.

The scientists also looked into the measures taken by SpaceX to reduce the brightness of Starlink satellites. Implemented in 2020, these measures include visors that prevent sunlight from illuminating too much of the satellite’s surface. These measures have served to reduce the brightness of Starlink satellites by a factor of 4.6, which means they’re now at a 6.8 magnitude (for reference, the brightest stars shine at a magnitude 1, and human eyes can’t see objects much dimmer than 6.0). This marks a major improvement, but it’s still not great, as members of the 2020 Satellite Constellations 1 workshop asked that satellites in LEO have magnitudes above 7.

The current study only considered the impacts of Starlink on the Zwicky Transient Facility. Every observatory will be affected differently by Starlink and other satellites, including the upcoming Vera C. Rubin Observatory, which is expected to be badly affected by megaconstellations. Observatories are also expected to experience problems as a result of radio interference, the appearance of ghost-like artifacts, among other potential issues.

More: Elon Musk Tweets Video of ‘Mechazilla’ Tower That Will Somehow Catch a Rocket.

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Earth's core is rapidly cooling, study reveals. Is our planet becoming 'inactive'? – USA TODAY

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Planet Earth hits 6th warmest year on record

Earth simmered to the sixth hottest year on record in 2021, according to several newly released temperature measurements. (Jan. 13)

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Earth’s interior is cooling faster than we previously estimated, according to a recent study, prompting questions about how long people can live on the planet.

There’s no exact timetable on the cooling process, which could eventually turn Earth solid, similar to Mars. But results from a new study, published in the peer-reviewed journal Earth and Planetary Science Letters, focuses on how quickly the core may cool by studying bridgmanite, a heat-conducting mineral commonly found at the boundary between the Earth’s core and mantle.

“Our results could give us a new perspective on the evolution of the Earth’s dynamics,”  ETH Zurich professor Motohiko Murakami, the lead author of the study, said in a press release. “They suggest that Earth, like the other rocky planets Mercury and Mars, is cooling and becoming inactive much faster than expected.”

While the process may be moving quicker than previously thought, it’s a timeline that “should be hundreds of millions or even billions of years,” Murakami told USA TODAY.

The boundary between the Earth’s outer core and mantle is where the planet’s internal heat interaction exists. The scientific team studied how much bridgmanite conducts from the Earth’s core and found higher heat flow is coming from the core into the mantle, dissipating the overall heat and cooling much faster than initially thought. 

“This measurement system let us show that the thermal conductivity of bridgmanite is about 1.5 times higher than assumed,” Murakami said in the press release. “We still don’t know enough about these kinds of events to pin down their timing.”

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