Sagittarius A* at the Center of Our Galaxy


A black hole called Sagittarius A* (pronounced A-star) lies at the center of our Milky Way Galaxy, only 27,000 light-years away. Its mass is roughly 4 million times the mass of the Sun. Our galaxy’s black hole is mild-mannered compared to the central black holes in some other galaxies, much more calmly consuming material around it. However, it does sometimes flare-up. An flareup lasting several hours is documented in this series of X-ray images from the orbiting Nuclear Spectroscopic Telescope Array (NuSTAR). NuSTAR is the first instrument to provide focused views of the area surrounding Sgr A* at X-ray energies higher than those accessible to the Chandra and XMM observatories. The flare sequence is shown in the panels on the right. The images cover a two-day span. X-rays are generated in material heated to over 100 million C and traveling at nearly the speed of light as it falls into the black hole. The center X-ray image spans about 100 light-years. Its bright white region is the hottest material closest to the black hole; the pinkish cloud probably belongs to the remnant of a nearby supernova. Click the picture to embiggen it.

Sgr A* is monitored on a daily basis by the X-ray telescope of the Swift satellite. I made contributions to the design of the power and thermal control systems of the Burst Alert Telescope instrument on Swift.

Image Credit: NASA

Kaboom


On  23 April, 2014, the rising tide of X-rays from a superflare on red dwarf DG CVn triggered the Swift satellite’s Burst Alert Telescope (BAT). The satellite turned to observe the source in greater detail with its other instruments and notified astronomers around the globe that a powerful outburst was in progress.

BTW, my principal contribution to the Swift satellite was the design and testing of the ultra-quiet power regulation system for the sensor array in the BAT.

Video Credit: NASA

Gamma Ray Bursts


Just before 2000 UTC on 14 January, the Fermi and Swift satellites detected a spike of gamma rays from the constellation Fornax. The missions alerted the astronomical community to the location of the burst, dubbed GRB 190114C. Ground-based facilities detected radiation with up to a trillion times the energy of visible light from the gamma-ray burst.

The illustration above shows the set-up for the most common type of GRB. The core of a massive star (left) has collapsed and formed a black hole. This “engine” drives a jet of particles that moves through the collapsing star and out into space at nearly the speed of light. The so-called prompt emission, which typically lasts a minute or less, may arise from the jet’s interaction with gas near the newborn black hole and from collisions between shells of fast-moving internal shockwaves within the jet itself. The afterglow emission occurs as the leading edge of the jet sweeps through the surroundings creating an external shock wave, and emitting radiation across a broad spectrum. That may continue for months to years in the case of radio and visible light and for hours at the highest gamma-ray energies yet observed.

Image Credit: NASA

Note: My principal contribution to the Swift satellite was the design and testing of the power regulation system for the X-ray detectors in Burst Alert Telescope.

A “Young” Supernova Remnant


g306_wideAstronomers estimate that a supernova explosion occurs perhaps a couple of times a century in the Milky Way. The expanding blast wave and hot stellar debris slowly dissipate over hundreds of thousands of years, eventually mixing with and becoming indistinguishable from interstellar gas. The Swift satellite uncovered the previously unknown remains of a shattered star during an X-ray survey of the galaxy’s central regions. The new object, named G306.3-0.9 after it’s coordinates in the sky,is among the youngest of the 300+ known supernova remnants in the Milky Way. Analysis indicates that G306.3–0.9 is probably less than 2,500 years old. That would make it one of the 20 youngest supernova remnants identified.

This composite image of G306.3–0.9 (the blob in the lower left) was stitched together using data from Chandra X-ray observations (blue), infrared data acquired by the Spitzer Space Telescope (red and cyan) and radio observations (purple) from the Australia Telescope Compact Array.

G306_Swift_XRTjpgThe image on the left was taken in February, 2011, using Swift’s X-ray Telescope as part of the Galactic Plane Survey. The dots in the image indicate where X-rays struck the detector. Despite this short 8.5-minute exposure, the extended circular patch of G306.3–0.9 stands out quite nicely.

Image Credits: NASA

NGC 3623


Here are two views of the nearby galaxy NGC 3623. The one on the left was taken using the UV telescope aboard the Swift satellite. The one on the right was taken with visible light. The galaxies spiral arms where new stars are being born stand out in the ultraviolet wavelengths emitted by hot baby stars.

Image Credits: NASA/Swift/L.McCauley, Penn State, CC BY-ND

A “Young” Supernova Remnant


g306_wideAstronomers estimate that a supernova explosion occurs perhaps a couple of times a century in the Milky Way. The expanding blast wave and hot stellar debris slowly dissipate over hundreds of thousands of years, eventually mixing with and becoming indistinguishable from interstellar gas. The Swift satellite uncovered the previously unknown remains of a shattered star during an X-ray survey of the galaxy’s central regions. The new object, named G306.3-0.9 after it’s coordinates in the sky,is among the youngest of the 300+ known supernova remnants in the Milky Way. Analysis indicates that G306.3–0.9 is probably less than 2,500 years old. That would make it one of the 20 youngest supernova remnants identified.

This composite image of G306.3–0.9 (the blob in the lower left) was stitched together using data from Chandra X-ray observations (blue), infrared data acquired by the Spitzer Space Telescope (red and cyan) and radio observations (purple) from the Australia Telescope Compact Array.

G306_Swift_XRTjpgThe image on the left was taken in February, 2011, using Swift’s X-ray Telescope as part of the Galactic Plane Survey. The dots in the image indicate where X-rays struck the detector. Despite this short 8.5-minute exposure, the extended circular patch of G306.3–0.9 stands out quite nicely.

Image Credits: NASA

Too Close for Comfort


Video Credit: NASA

UPDATE—A personal note: I contributed to the design of components of the Burst Alert Telescope instrument on Swift. My contributions include the ultra-quiet power regulators for the detectors in the instrument, the variable high-voltage supply for the detectors, and the pulse-width-modulation regulator for the thermal control system of the BAT. The same PWM regulator was also used in other locations on the satellite.

Gamma Ray Burst


When a massive star collapses to form a black hole, a burst of gamma rays results as particles are blasted outward at nearly the speed of light. This animation shows the most common type of gamma-ray burst. An end-on view of a jet greatly boosts its apparent brightness. One especially bright burst (GRB 130427A) was detected in 2013 by the Fermi and Swift satellites. A Fermi image of that burst ends the animation sequence.

Video Credit: NASA

Detecting a Supernova


Beforem82_uvot_before_sn_largeAfterm82_uvot_after_sn_large-arrow_0These Swift Ultraviolet optical telescope images show a galaxy called M82 before and after the new supernova. The pre-explosion view combines data taken between 2007 and 2013. The view showing SN 2014J (arrow) merges three exposures taken on 22 January, 2014. Mid-ultraviolet light is shown in blue, near-UV light in green, and visible light in red. The image is slightly more than half the apparent diameter of a full moon across.

This is a Type Ia supernova, the total destruction of a white dwarf star by one of two possible scenarios. In one, the white dwarf orbits a normal star, pulls a stream of matter from it, and gains mass until it reaches a critical threshold and explodes. In the other, the blast arises when two white dwarfs in a binary system eventually spiral inward and collide.

In either case, the explosion produces a superheated shell of plasma that expands outward into space at tens of millions of miles an hour. The interactions between the shell’s size, transparency and radioactive heating control when the supernova reaches peak brightness. Astronomers expect SN 2014J to continue brightening for a few more weeks. It may be visible in binocular by early February.

M82 (aka the Cigar Galaxy) is located in the constellation Ursa Major and is a popular target for small telescopes. It’s undergoing a period of extensive star formation that makes it many times brighter than our own Milky Way galaxy.

Image Credit: NASA

A UV View of Andromeda


This mosaic of M31 merges 330 individual images taken by the Ultraviolet/Optical Telescope aboard the Swift spacecraft. It is the highest-resolution image of the galaxy ever recorded in the ultraviolet. Also known as the Andromeda Galaxy, M31 is more than 220,000 light-years across and lies 2.5 million light-years away. On a clear, dark night, the galaxy is faintly visible as a misty patch to the naked eye.

The irregular shape of the image results when the more than 300 images were assembled to make the final image.

There are three instruments on Swift—a UV telescope, an X-ray telescope, and the Burst Alert Telescope which serves as the gamma ray burst detector for the spacecraft. I contributed to the design of the ultra-quiet regulators powering the detector blocks in the BAT.

Image Credit: NASA /Swift / Stefan Immler (GSFC) and Erin Grand (UMCP)

A Stellar Death Spiral


Roughly 290 million years ago, a star more or less like the Sun got too close to the central black hole of its galaxy. Intense tides tore the star apart and the resulting outburst of visible, ultraviolet and X-ray light first reached Earth in 2014. Observations from the Swift satellite have mapped out how and where these different wavelengths were produced as the shattered star’s debris circled the black hole. This animation illustrates how debris from a tidally disrupted star collided with itself, creating shock waves that emit ultraviolet and visible light. According to the Swift observations, that debris then took about a month to fall back to the black hole, where they produced changes in its X-ray emission that correlated with the earlier UV and visible light bursts.

Video Credit: NASA

V404 Cygni


On June 15, the Swift satellite caught the onset of a rare X-ray outburst from a stellar-mass black hole in the binary system V404 Cygni. In that system a stream of gas from a star much like the sun flows toward a 10 solar mass black hole. Instead of spiraling into the black hole, the gas accumulates in an accretion disk around it. Every couple of decades, the disk changes state, sending the gas rushing inward. The result is a new X-ray outburst.

[youtube https://www.youtube.com/watch?v=fCWteTkhd_A]

Video Credit: NASA

Swift’s Gamma Ray Burst Number 1,000


grb151027b_uvot_xrt_labeled_2160GRB 151027B, Swift‘s 1,000th burst, is in the center of this composite X-ray, ultraviolet, and optical image. X-rays were captured by Swift‘s X-Ray Telescope within minutes after the Burst Alert Telescope detected the blast. Swift‘s Ultraviolet/Optical Telescope (UVOT) began observations a few seconds later and faintly detected the burst in visible light. The image includes X-rays with energies from 300 to 6,000 eV, mostly from the burst, and lower-energy light seen through the UVOT’s visible, blue and ultraviolet filters (color shifted, respectively, to red, green and blue).

Image Credit: NASA

Rings Around a Black Hole


V404 Cygni Black HoleV404 Cygni is a binary system that contains an erupting black hole. These rings of x-ray light centered on that system were imaged by the x-ray telescope aboard the Swift satellite. Color indicates the energy of the X-rays, with red representing the lowest (800 to 1,500 electron volts, eV), green for medium (1,500 to 2,500 eV), and blue for the most energetic (2,500 to 5,000 eV). Visible light has energies ranging from about 2 to 3 eV. The dark lines running diagonally through the image are artifacts of the imaging system.

Image Credits: Andrew Beardmore (Univ. of Leicester) and NASA