Hubble Solves Cosmic ‘Whodunit’ with Interstellar Forensics

Hubble Measures Content of the Leading Arm of the Magellanic Stream
Credits:Illustration: D. Nidever et al., NRAO/AUI/NSF and A. Mellinger, Leiden-Argentine-Bonn (LAB) Survey, Parkes Observatory, Westerbork Observatory, Arecibo Observatory, and A. Feild (STScI). Science: NASA, ESA, and A. Fox (STScI).  Release Image
On the outskirts of our galaxy, a cosmic tug-of-war is unfolding—and only NASA’s Hubble Space Telescope can see who’s winning.
The players are two dwarf galaxies, the Large Magellanic Cloud and the Small Magellanic Cloud, both of which orbit our own Milky Way Galaxy. But as they go around the Milky Way, they are also orbiting each other. Each one tugs at the other, and one of them has pulled out a huge cloud of gas from its companion.
Called the Leading Arm, this arching collection of gas connects the Magellanic Clouds to the Milky Way. Roughly half the size of our galaxy, this structure is thought to be about 1 or 2 billion years old. Its name comes from the fact that it’s leading the motion of the Magellanic Clouds.
The enormous concentration of gas is being devoured by the Milky Way and feeding new star birth in our galaxy. But which dwarf galaxy is doing the pulling, and whose gas is now being feasted upon? After years of debate, scientists now have the answer to this “whodunit” mystery.
“There’s been a question: Did the gas come from the Large Magellanic Cloud or the Small Magellanic Cloud? At first glance, it looks like it tracks back to the Large Magellanic Cloud,” explained lead researcher Andrew Fox of the Space Telescope Science Institute in Baltimore, Maryland. “But we’ve approached that question differently, by asking: What is the Leading Arm made of? Does it have the composition of the Large Magellanic Cloud or the composition of the Small Magellanic Cloud?”
Fox’s research is a follow-up to his 2013 work, which focused on a trailing feature behind the Large and Small Magellanic Clouds. This gas in this ribbon-like structure, called the Magellanic Stream, was found to come from both dwarf galaxies. Now Fox wondered about its counterpart, the Leading Arm. Unlike the trailing Magellanic Stream, this tattered and shredded “arm” has already reached the Milky Way and survived its journey to the galactic disk.
The Leading Arm is a real-time example of gas accretion, the process of gas falling onto galaxies. This is very difficult to see in galaxies outside the Milky Way, because they are too far away and too faint. “As these two galaxies are in our backyard, we essentially have a front-row seat to view the action,” said collaborator Kat Barger at Texas Christian University.
In a new kind of forensics, Fox and his team used Hubble’s ultraviolet vision to chemically analyze the gas in the Leading Arm. They observed the light from seven quasars, the bright cores of active galaxies that reside billions of light-years beyond this gas cloud. Using Hubble’s Cosmic Origins Spectrograph, the scientists measured how this light filters through the cloud.
In particular, they looked for the absorption of ultraviolet light by oxygen and sulfur in the cloud. These are good gauges of how many heavier elements reside in the gas. The team then compared Hubble’s measurements to hydrogen measurements made by the National Science Foundation’s Robert C. Byrd Green Bank Telescope at the Green Bank Observatory in West Virginia, as well as several other radio telescopes.
“With the combination of Hubble and Green Bank Telescope observations, we can measure the composition and velocity of the gas to determine which dwarf galaxy is the culprit,” explained Barger.
After much analysis, the team finally had conclusive chemical “fingerprints” to match the origin of the Leading Arm’s gas. “We’ve found that the gas matches the Small Magellanic Cloud,” said Fox. “That indicates the Large Magellanic Cloud is winning the tug-of-war, because it has pulled so much gas out of its smaller neighbor.”
This answer was possible only because of Hubble’s unique ultraviolet capability. Because of the filtering effects of Earth’s atmosphere, ultraviolet light cannot be studied from the ground. “Hubble is the only game in town,” explained Fox. “All the lines of interest, including oxygen and sulfur, are in the ultraviolet. So if you work in the optical and infrared, you can’t see them.”
Gas from the Leading Arm is now crossing the disk of our galaxy. As it crosses, it interacts with the Milky Way’s own gas, becoming shredded and fragmented.
This is an important case study of how gas gets into galaxies and fuels star birth. Astronomers use simulations and try to understand the inflow of gas in other galaxies. But here, the gas is being caught red-handed as it moves across the Milky Way’s disk. Sometime in the future, planets and solar systems in our galaxy may be born out of material that used to be part of the Small Magellanic Cloud.
The team’s study appears in the Feb. 20 issue of The Astrophysical Journal.
As Fox and his team look ahead, they hope to map out the full size of the Leading Arm—something that is still unknown.
The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.

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Ann Jenkins / Ray Villard 
Space Telescope Science Institute, Baltimore, Maryland 
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Andrew Fox
Space Telescope Science Institute, Baltimore, Maryland 

Source: HubbleSite/News 

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Rooting for Answers: Simulating G-Force to Test Plant Gravity Perception in Mustard Seedlings

ISS – Veggie Mission patch.

March 21, 2018

When plants on Earth search for nutrients and water, what drives their direction? Very simply, gravitational force helps them find the easiest path to the substances they need to grow and thrive. What happens if gravity is no longer part of the equation?

Botanists from Ohio Weslyan University leverage the microgravity environment of the International Space Station to study root growth behaviors and sensory systems in an investigation known as Gravity Perception Systems (Plant Gravity Perception). The researchers look for adaptability to microgravity and measure overall sensitivity to simulated gravity for two strains of mustard seedlings, including Arabidopsis thaliana Wild Type and a starchless genetic variant. Within the wild type, starch acts like a weight, falling within the root tips and driving them toward the Earth.

Image above: Seeds are aligned along a membrane within the cassette and germinated before their exposure to simulated gravity within the EMCS. Image Credit: NASA.

As the lead investigator for Plant Gravity Perception, botanist Chris Wolverton describes the investigation’s central question: “We want to know – what’s the least amount of gravity plants can detect to cause the falling of heavy [starchy] bodies in their cells?”

The study exposes both strains to incremental amounts of gravity ranging from four one thousandths or 0.004G – all the way up to one G. By comparison, gravitational force experienced on Earth is a constant one G.

Why include two types of seedlings? While exact thresholds for starchy strains are poorly understood, response mechanisms for starchless genetic variants are even more of a mystery.

Plant Gravity Perception uses acceleration from the European Modular Cultivation System (EMCS) to simulate gravity. Seedlings are first placed in seed cassettes, then aligned along radial blades of a centrifugal rotor. This lets investigators control the intensity of gravity experienced at any point along the rotational arms, testing hundreds of fractional degrees of gravity at a single time through controlled spins.

Image above: Arabidopsis growth within EMCS seed cassettes. Image Credit: Chris Wolverton.

Much like the popular rides at carnivals that spin riders and cause them to “stick” to the walls, this investigation steadily increases g-force exposure to test the outer boundaries of seedlings’ perceptual abilities. As the arms of the centrifuge spin, scientists hope to pinpoint exactly where growth response begins.

Most interesting of all may be the starchless plants’ responses. Even for those without starch, the mutant form of the seedlings may still retain the same sensory perception system as their cousins. These plants may still sense gravity but respond only at higher thresholds, be unable to move at all, or use entirely different cues to determine growth direction. When the centrifuge’s acceleration is turned off, scientists can also measure seedling response to microgravity and establish a baseline.

As photosynthetic organisms, plants are also very sensitive to light cues for growth. Using directed lights, Plant Gravity Perception is providing additional growth cues at varying points to test relationship between light perception and gravity perception. Back at home, botanists can watch the footage to assess responses.

Image above: Seed cassettes used for loading samples in the EMCS are developed and tested by NASA AMES. Image Credit: Chris Wolverton.

Even though the orbiting laboratory is regularly resupplied, crew members must consume fresh deliveries quickly. To supplement a large supply of shelf stable foods, space station investigations such as Veg-03 enable astronauts to act as gardeners and supplement their diets with the hopes of adding nutritional variety and reducing resupply payload weight dedicated to food stores.

While seedlings from Plant Gravity Perception will not wind up on astronauts’ plates, their studied growth furthers our knowledge of perceptual thresholds and makes selecting appropriate garden greens likely to thrive in space easier for future long duration spaceflight, including exploration missions beyond low-Earth orbit.

For Earth, Wolverton notes that gravity perception in roots “influences how efficient a plant is, how responsive it is to drought conditions, to flooding, to fertilizer.”

Rooting for Answers: Simulating G-Force in Plants

He adds, “If we understood better how [gravity is] perceived… that opens up a whole source of trait breeding and genetic variation that we can look to.” This would allow agriculturalists to select root growth appropriate for different fertilization levels, soil composition and environmental extremes.

Related links:

Plant Gravity Perception:

European Modular Cultivation System (EMCS):


Spot the Station:

Space Station Research and Technology:

International Space Station (ISS):

Images (mentioned), Video (NASA), Text, Credits: NASA/Michael Johnson/JSC/Morgan McAllister.

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