2018 November 15 Comet 46P/Wirtanen Image Credit &…

2018 November 15

Comet 46P/Wirtanen
Image Credit & Copyright: Alex Cherney (Terrastro, TWAN)

Explanation: Periodic Comet 46P/Wirtanen is now the brightest comet in the night sky, but too faint to be seen by eye. From dark sky sites it could just become naked-eye visible though, as it’s 5.4 year long looping orbit takes it closest to Earth and the Sun in mid December. Fluorescing in sunlight, its spherical coma is about half the angular size of a full moon in this southern hemisphere telescopic view from November 7. Then the comet was about 2 light-minutes away or 35 million kilometers from Earth-bound telescopes, so the pretty greenish coma seen here is around 150,000 kilometers across. That makes it about the size of Jupiter. The stack of digital images also reveals a very faint tail extending toward 4 o’clock with a distant background galaxy notable at the upper left. As a regular visitor to the inner Solar System, comet 46P/Wirtanen was once the favored rendezvous target for ESA’s comet exploring Rosetta mission.

∞ Source: apod.nasa.gov/apod/ap181115.html

NASA’s Webb Telescope Will Investigate Cosmic Jets From Young Stars

A pair of jets protrude outwards in this infrared image of Herbig-Haro 212 (HH 212), taken by the European Southern Observatory’s Very Large Telescope. Webb’s high resolution and sensitivity will allow astronomers to examine objects like this in greater detail than ever before. Credits: ESO/M. McCaughrean

The formation of a star sounds like a simple process: a cloud of gas collapses in on itself, growing denser and hotter until nuclear fusion ignites and a star begins to shine. The reality is more complex and dramatic.
Swirling gas spins faster and faster, threatening to rip the still-forming star into pieces. Clumps of matter are captured within a tangle of magnetic fields and squirt outward at supersonic speeds. All of it happens within a dusty shroud that blocks visible light. NASA’s James Webb Space Telescope will penetrate that dusty veil and reveal new secrets of star birth.
As an interstellar gas cloud contracts, it spins more rapidly, just as a twirling ice skater does when she draws in her arms. The only way for the gas to continue moving inward is for some of the spin (known as angular momentum) to be removed.

In a process that’s still not fully understood, magnetic fields funnel some of the swirling material into twin jets that shoot outward in opposite directions. These jets travel at speeds of hundreds of miles per second and spread across light-years of space.

“Jets are signposts of star formation,” said Tom Ray, an astronomer at the Dublin Institute for Advanced Studies. Ray and many other scientists are planning to use Webb to study these jets and stellar outflows. Their goals include learning more about how stars form, and how their jets interact with the surrounding interstellar medium of gas and dust.


Over the span of 14 years, the Hubble Space Telescope looked at a bright, clumpy jet known as HH 34 ejected from a young star. Several bright regions in the clumps signify where material is slamming into each other, heating up, and glowing. Credits: NASA, ESA, P. Hartigan (Rice University), and G. Bacon (STScI)

Shock Waves in Space

They will study objects like Herbig-Haro (HH) 212, located about 1,400 light-years away in the constellation Orion. At the center of HH 212 resides a still-forming star or protostar that will eventually grow to become about the mass of our Sun. Jets from the protostar extend across about 5 light-years of space.
The material in those jets is traveling at supersonic speeds. When it slams into surrounding material, it creates a shock wave, much like the “sonic boom” of a supersonic aircraft. The shock heats the interstellar gas, causing it to glow at specific wavelengths of light that depend on the conditions within the shock wave itself.
“With Webb, we’ll be able to dissect the interactions of the protostar with its surroundings that were previously blurred into a single blob,” said Ewine van Dishoeck of Leiden University.
Webb’s exquisite angular resolution will allow it to pick up the tiniest details. This will allow it to see solar-system-scale features at the distance of objects like HH 212. And since the farther along a jet you go from the protostar, the longer the time since the material was ejected, astronomers can probe the history of the star’s matter-gathering or accretion process.
“Webb has higher sensitivity and higher angular resolution at long infrared wavelengths than anything we could do previously. Webb will answer questions we can’t answer from the ground,” said Alberto Noriega-Crespo of the Space Telescope Science Institute.
Webb also will precisely discern different wavelengths of infrared light. This will allow it to detect infrared light from a variety of chemical elements associated with the shock wave, including iron, neon and sulfur.
When a jet of material traveling at supersonic speeds slam into interstellar gas and dust, it creates a shock wave that compresses and heats matter.  Credits: NASA and J. Olmsted (STScI). Hi-res image
A New Star Emerges
HH 212 is about 100,000 years old. Over the course of the next million years, its protostar will gather a sun’s worth of gas. The remainder of the surrounding material will either condense into planets or get swept away by outflows and other processes. Eventually, a fully formed star will emerge.
“By studying HH 212, and objects like it, we want to learn how jets and outflows help the star escape from its cocoon,” said Mark McCaughrean of the European Space Agency.
The observations described here will be taken as part of Webb’s Guaranteed Time Observation (GTO) program. The GTO program provides dedicated time to the scientists who have worked with NASA to craft the science and instrument capabilities of Webb throughout its development.
The James Webb Space Telescope will be the world’s premier space science observatory when it launches in 2021. Webb will solve mysteries of our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international project led by NASA with its partners, the European Space Agency (ESA) and the Canadian Space Agency.

For more information about Webb, visit www.nasa.gov/webb

By Christine Pulliam
Space Telescope Science Institute, Baltimore, Md.

Editor: Lynn Jenner


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