Mixing Science and Art, One Painting at a Time

All her life, Laci Shea Brock has needed to be creative and inventive. So, perhaps it’s not completely surprising that in addition to pursuing her PhD in planetary sciences and astrophysics, she’s also a talented artist.

“My Dad says I’ve always had a paintbrush in my hand,” Brock said, “and I’ve always been inspired by space and nature.

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The Destruction of Dark Matter isn’t Causing Extra Radiation at the Core of the Milky Way

There are times when it feels like dark matter is just toying with us. Just as we gather evidence that hints at one of its properties, new evidence suggests otherwise. So it is with a recent work looking at how dark matter might behave in the center of our galaxy.

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Supercomputer Simulation Shows a Supernova 300 Days After it Explodes

The answers to many questions in astronomy are hidden behind the veil of deep time. One of those questions is around the role that supernovae played in the early Universe. It was the job of early supernovae to forge the heavier elements that were not forged in the Big Bang. How did that process play out? How did those early stellar explosions play out?

A trio of researchers turned to a supercomputer simulation to find some answers.

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Detecting the Neutrinos From a Supernova That’s About to Explode

Neutrinos are puzzling things. They’re tiny particles, almost massless, with no electrical charge. They’re notoriously difficult to detect, too, and scientists have gone to great lengths to detect them. The IceCube Neutrino Observatory, for instance, tries to detect neutrinos with strings of detectors buried down to a depth of 2450 meters (8000 ft.) in the dark Antarctic ice.

How’s that for commitment.

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Neutron Stars Could Have a Layer of Exotic Quark Matter Inside Them

Neutron stars are strange things. They can form when gravity kills a star, crushing its remains into a dense ball the size of a small city. They are so dense that only quantum forces and the Pauli exclusion principle keeps it from collapsing into a black hole singularity. The interior of a neutron star is so dense that matter behaves in ways we still don’t fully understand.

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The Lowest Mass Black Hole has Been Found, only 3.3 Times the Mass of the Sun

Black holes are one of the most awesome and mysterious forces of nature. At the same time, they are fundamental to our understanding of astrophysics. Not only are black holes the result of particularly massive stars that go supernova at the end of their lives, they are also key to our understanding of General Relativity and are believed to have played a role in cosmic evolution.

Because of this, astronomers have diligently been trying to create a census of black holes in the Milky Way galaxy for many years. However, new research indicates that astronomers may have overlooked an entire class of black holes. This comes from a recent discovery where a team of astronomers observed a black hole that is just over three Solar masses, making it the smallest black hole discovered to date.

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SOFIA Follows the Sulfur for Clues on Stellar Evolution

The high-flying SOFIA telescope is shedding light on where some of the basic building blocks for life may have originated from. A recent study published on The Astrophysical Journal: Letters led by astronomers from the University of Hawaii, including collaborators from the University of California Davis, Johns-Hopkins University, the North Carolina Museum of Natural Sciences, Appalachian State University, and several international partners (including funding from NASA), looked at a lingering mystery in planet formation: the chemical pathway of the element sulfur, and its implications and role in the formation of planets and life.

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GW170817 Update: Surprises From First Gravitational Wave Observed Independently

“This is quite literally a physics gold mine!” said Masao Sako, with the University of Pennsylvania.

For over a week now, the astronomy and astrophysics communities have been buzzing with the news of the latest gravitational wave discovery. And this discovery has been big.

Four days before the Great American Solar Eclipse on August 21, a newly discovered gravitational wave caused more astronomers (8,223+), using more telescopes (70), to publish more papers (100 — see the list below) in less time than for any other astronomical event in history. The sixth gravitational wave (GW) to be discovered by the Laser Interferometer Gravitational-wave Observatory (LIGO) and Virgo GW observatories, which occurred on August 17, 2017 at 12:41:04 UTC, was surprising in two ways already reported.

GW event six, designated GW170817, did not result from the collision and subsequent explosion of two black holes. All previous GW events, including the first ever discovered in 2015, had involved the collision of black holes with typically 40 times the mass of the Sun between them. Here however, the GW was evidently triggered by the collision and explosion of two neutron stars, having only 3 times the Sun’s mass in total.

Afterglow of GW170817 is shown in close-ups captured by the NASA Hubble Space Telescope, showing it dimming in brightness over days and weeks. CREDIT: NASA and ESA: A. Levan (U. Warwick), N. Tanvir (U. Leicester), and A. Fruchter and O. Fox (STScI)

Crucially, GW170817 occurred ten times closer to Earth than all earlier GW events. Earlier GWs involved black hole collisions at more than 1.3 billion light-years (400 million parsecs or Mpc). GW170817, in comparison, was known within hours of its discovery to lie within only 130 million light-years (40 Mpc). That vastly improved astronomer’s odds of detecting the event independently, because in cosmological terms, it occurred within less than 1% of the universe’s Hubble length of 14 billion light-years (4,300 Mpc).

Not widely reported is that our current astronomical theory regarding GW170817 still depends significantly on observations yet to be made. In brief, astronomers currently believe that GW170817 was triggered by the merger of two neutron stars, which triggered the explosion of a Short Gamma-Ray Burst (SGRB), which emitted only a fraction of the gamma-ray energy in our direction normally associated with SGRBs, because it was the first SGRB observed at such a large angle away from the direction of its focused jets of gamma-rays. The SGRB associated with GW170817 emitted its jet at roughly 30 degrees away from our line-of-sight. All other SGRBs have been observed at only a few degrees from alignment with their jets. The exact angle of the newly discovered SGRB’s jet is important in understanding how its afterglow compares with other SGRB afterglows. Significant properties reported for the GW, including its distance, depend on the angle at which the two neutron stars collided relative to Earth.

The collision angle determined roughly based on the GW itself is probably OK. Only radio maps of the SGRB region at 100 days however, will provide astronomers with the most precise measurements of the resulting explosion’s velocities and directions over time to date. Only then will astronomers learn more about the exact angle of the SGRB’s jet, providing potentially a more accurate estimate of the angle at which the neutron stars collided. More surprises could be in store as a result, including refinements of the properties reported.

ANIMATION (you may have to click image for animation in some browsers): This time-lapse image of the afterglow of GW170817 shows it continuing to increase in radio wavelength brightness over the first month, and was provided by the National Radio Astronomy Observatory Very Large Array radio telescope. CREDIT: NRAO/VLA

Unlike previous events, GW170817 was close enough that within 1.74 seconds of its initial detection by LIGO, it’s gamma radiation was detected by the Fermi Gamma-Ray space telescope. The INTEGRAL Gamma-Ray space observatory detected it too, and it was later designated SGRB 170817A. As an SGRB alone, the event would have triggered alerts to observatories worldwide and aloft, each aiming to detect the explosion’s faint optical afterglow. SGRB optical afterglows have been used to pinpoint the exact positions of SGRBs, not only on the sky, but also in terms of their distance from Earth.

Astronomers in this case had the first GW ever to coincide with, and be independently corroborated by, any observable counterpart, and alerts became a call to astronomical arms. Even though its exact position on the sky was uncertain by many degrees, GW170817 was so close that astronomers were able to quickly narrow down its exact location.

“With a previously-compiled list of nearby galaxies having positions and distances culled from the massive on-line archive of the NASA/IPAC Extragalactic Database (NED), our team rapidly zeroed in on the host galaxy of the event,” said Barry Madore, of Carnegie Observatories.

Precisely because GW170817 occurred at only 130 million light-years, the number of candidate galaxies to observe was only several dozen. In contrast, for previous GW discoveries occurring at billions of light-years, thousands of galaxies would have to be observed. Within 11 hours of the explosion, its afterglow was discovered in the lenticular galaxy NGC 4993, by the Swope 1-m telescope in Chile. They obtained the first-ever visual image of an event associated with a GW.

“Where observation is concerned, chance favors only the prepared mind,” added Madore, quoting Louis Pasteur from 150 years ago. Madore is also a researcher with the Swope team and a co-author on six papers reporting Swope’s discovery of the afterglow and some of its implications. “When alerts were sent out to the LIGO/VIRGO gravity wave detection consortium on the night of August 17, 2017, our team of astronomers was indeed prepared.”

New images of the afterglow of GW170817, aka SGRB 170817A, initially designated as Swope Supernova Survey SSS17a, revealed a bright blue astronomical transient, later designated as AT2017gfo by the International Astronomical Union (IAU).

“There will be more such events, no doubt; but this image taken at the Henrietta Swope 1m telescope at the Las Campanas Observatory in Chile was the first in history, and it truly ushered in the Era of Multi-Messenger Astronomy,” said Madore.

Radio observatories joined the hunt, including the Karl G. Jansky Very Large Array (VLA), the Australia Telescope Compact Array (ATCA) and the Giant Metrewave Radio Telescope (GMRT). So did the Swift ultraviolet and Chandra X-ray space observatory satellites. By day one after the explosion, all frequencies of the electromagnetic spectrum were being observed in the direction of NGC 4993. On multiple wavelengths, multiple “messengers” of GW170817’s existence began to reveal more than the sum of their parts.

Change in brightness of GW170817’s afterglow over time since explosion (merger), is shown in these light-curves. Brightness in 14 different optical wavelengths is shown, including invisible ultraviolet, and visible blue, green, and yellow, and invisible infrared wavelengths in orange and red. Afterglow fades quickly in all wavelengths, except infrared. In infrared, afterglow continues to brighten until ~3 days after explosion, before beginning to fade. CREDIT: Las Campanas Observatory, Carnegie Institution of Washington (Swope + Magellan)

AT2017gfo brightened over the next few days after explosion, in near infrared observations continued by Swope. Their light-curves show the changes in the afterglow’s brightness over time. At three days post explosion, the near-infrared afterglow stops brightening and begins to fade. As with other SGRB afterglows, AT2017gfo faded completely from visual observation over the course of days to weeks, but observations in X-rays and radio continue. Radio observations at 100 days post explosion, which will not occur until November 25, are crucial as said. Although a month away, planned radio observations will determine more than just the long-term evolution of the afterglow over 3 months. Indeed, our astronomical theory accounting for the event’s first three weeks, as already observed, analyzed, and reported, still depends to a surprising degree on an exact number of degrees. The number of degrees relative to Earth for this SGRB based on radio data however, will not be known for at least a month.

“With GW170817 we have for the first time truly independent verification of a gravitational wave source,” said Robert Quimby, of the Kavli Institute for the Physics and Mathematics of the Universe at the University of Tokyo, and coauthor of a paper regarding the event’s implications. “The electromagnetic signature of this event can be uniquely matched to the predictions of binary neutron star mergers, and it is actually quite amazing how well the theory matches the data considering how few observational constraints were available to guide the model.”

“With GW170817, we can learn about nuclear physics, relativity, stellar evolution, and cosmology all in one shot,” added Sako, who is also a co-author on ten papers regarding the event. “Plus we now know how all of the heaviest elements in the Universe are created.”

Afterglow faded from optical observations over days to weeks. Here, however, as observed at radio frequencies by the Very Large Array radio telescope, the electromagnetic counterpart to GW170817 is seen brightening over the first month since explosion. CREDIT: Courtesy of Gregg Hallinan, California Institute of Technology, and the National Radio Astronomy Observatory Very Large Array radio telescope

EVENT CHRONOLOGY

T = 0 sec.: GW170817 detected by LIGO/VIRGO [1, 82]
T = 1.74 sec.: SGRB 170817A detected by Fermi Gamma-Ray Burst Monitor satellite immediately after GW170817 [52]
T = 28 min.: Gamma-ray Coordinates Network (GCN) Notice [53]
T = 40 min.: GCN Circular [53]
T = 5.63 hr.: First sky map locating GW170817 to within several degrees [53]
T = 10.9 hr.: Swope 1-m observatory discovers explosion’s afterglow, AT 2017gfo, in galaxy NGC 4993 [18, 24, 64, 75, 77]
T = 11.09 hr.: PROMPT 0.4m observatory detects AT 2017gfo [88]
T = 11.3 hr.: Hubble Space Telescope images AT 2017gfo [20]
T = 12-24 hr.: Magellan; Las Campanas Observatory; W. M. Keck Observatory; Blanco 4-m Cerro Tololo Inter-American Observatory; Gemini South; European Southern Observatory VISTA; Subaru among 6 Japanese telescopes; Pan-STARRS1; Very Large Telescope; 14 Australian telescopes; and Antarctic Survey Telescope optical observatories, and VLA, VLITE, ATCA, GMRT, and ALMA radio observatories, as well as Swift and NuSTAR ultraviolet satellite observatories

PROPERTIES

Position: Right Ascension 13h09m48.085s ± 0.018s; Declination -23d22m53.343s ± 0.218s (J2000 equinox); 10.6s or 7,000 light-years (2.0 kiloparsecs or kpc) from the nucleus of lenticular galaxy NGC 4993 [18]
Distance: 140 ± 40 million light-years (41 ± 13 Mpc), with 30% scatter based on 3 GW-based estimates [1, 25, 82], and 131 ± 9 million light-years (39.3 ± 2.7 Mpc), with 7% scatter based on 3 distance indicators, including GW-based as well as new Fundamental Plane relation-based distances for NGC 4993 [41, 43], and Tully-Fisher relation-based distances for galaxies in the group of galaxies including NGC 4993 from the NASA/IPAC Extragalactic Database (NED)
Mass: Neutron stars total 2.82 +0.47 -0.09 Sun’s mass [82]; mass ejected in elements heavier than iron is 0.03 ± 0.01 Sun’s mass or 10,000 Earth masses, based on 4 estimates [24, 59, 82, 93], including gold amounting to 150 ± 50 Earth masses [60]
Luminosity: Peaks at 0.5 days after explosion, at ~1042 erg/s, equivalent to 260 million Suns [24]
SGRB jet angle: 31 ± 3 degrees away from line-of-sight to Earth, based on 9 estimates [2, 25, 34, 35, 36, 44, 58, 62, 82]
SGRB jet speed: 30% speed of light, based on 4 estimates [20, 42, 59, 75]
Names: GW170817, SGRB 170817A, AT 2017gfo = IAU designation for SGRB afterglow, aka SSS17a, DLT17ck, J-GEM17btc, and MASTER OTJ130948.10-232253.3

IMPLICATIONS

Astronomy (1): Confirms binary neutron star collisions as a source for GW and SGRB events [1, 82]
Astronomy (2): GWs provide a new way of measuring neutron star diameters [8]
Astronomy (3): Gives universal expansion rate, or Hubble constant, as H0 = 71 ± 10 km -1 Mpc-1, with 14% accuracy, based on 6 GW-based estimates for GW170817 ranging from 69 to 74 km -1 Mpc-1, bridging current estimates [1, 22, 36, 60, 74, 82]; accuracy will improve to 4% with future similar events [74]
General Relativity (1): Confirms GW velocity equals speed of light to within 1 part per 1,000,000,000,000,000 or 1/1015 [7, 21, 70, 91]
General Relativity (2): Confirms equivalence of gravitational energy and inertial energy, or Weak Equivalence Principle, to within 1 part per 1,000,000,000 or 1/109 [7, 11, 91, 92]
Physics: Confirms binary neutron star collisions are significant production sites for elements heavier than iron, including gold, platinum, and uranium [17, 69]
Life on Earth: Indicates a higher deadly rate of gamma-rays for extraterrestrial life [15]
GW170817 (1): Predicted one binary neutron star collision per year similar to GW170817 within a distance from Earth of 130 million light-years [40 Mpc] [24]
GW170817 (2): Predicted to produce a 10 Giga-Hertz afterglow that peaks at ~100 days with a radio magnitude of ~10 milli-Janskys [24]
GW170817 (3): Predicted to remain visible in radio for 5-10 years, and for decades with next-generation radio observatories [2]

BIBLIOGRAPHY

96 papers on GW170817 released on arXiv during week of October 16-20

1. Abbott, B. P. et al., A gravitational-wave standard siren measurement of the Hubble constant, Nature, arXiv:1710.05835
2. Alexander, K. D. et al., The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/VIRGO GW170817. VI. Radio Constraints on a Relativistic Jet and Predictions for Late-Time Emission from the Kilonova Ejecta, ApJL, arXiv:1710.05457
3. Andreoni, I. et al., Follow up of GW170817 and its electromagnetic counterpart by Australian-led observing programs, PASA, arXiv:1710.05846
4. ANTARES, IceCube, Pierre Auger, LIGO Scientific, Virgo Collaborations, Search for High-energy Neutrinos from Binary Neutron Star Merger GW170817 with ANTARES, IceCube, and the Pierre Auger Observatory, na, arXiv:1710.05839
5. Arcavi, I. et al., Optical emission from a kilonova following a gravitational-wave-detected neutron-star merger, Nature, arXiv:1710.05843
6. Arcavi, I. et al., Optical Follow-up of Gravitational-wave Events with Las Cumbres Observatory, ApJL, arXiv:1710.05842
7. Baker, T. et al., Strong constraints on cosmological gravity from GW170817 and GRB 170817A, na, arXiv:1710.06394
8. Bauswein, A. et al., Neutron-star radius constraints from GW170817 and future detections, ApJL, submitted, arXiv:1710.06843
9. Belczynski, K. et al., GW170104 and the origin of heavy, low-spin binary black holes via classical isolated binary evolution, A&A, arXiv:1706.07053
10. Blanchard, P. K. et al., The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/VIRGO GW170817. VII. Properties of the Host Galaxy and Constraints on the Merger Timescale, ApJL, arXiv:1710.05458
11. Boran, S. et al., GW170817 Falsifies Dark Matter Emulators, na, arXiv:1710.06168
12. Brocato, E. et al., GRAWITA: VLT Survey Telescope observations of the gravitational wave sources GW150914 and GW151226, MNRAS, submitted, arXiv:1710.05915
13. Bromberg, O. et al., The gamma-rays that accompanied GW170817 and the observational signature of a magnetic jet breaking out of NS merger ejecta, MNRAS, arXiv:1710.05897
14. Buckley, D. A. H. et al., A comparison between SALT/SAAO observations and kilonova models for AT 2017gfo: the first electromagnetic counterpart of a gravitational wave transient – GW170817, MNRAS, arXiv:1710.05855
15. Burgess, J. M. et al., Viewing short Gamma-ray Bursts from a different angle, na, arXiv:1710.05823
16. Chang, P.; & Murray, N., GW170817: A Neutron Star Merger in a Mass-Transferring Triple System, MNRAS Letters, arXiv:1710.05939
17. Chornock, R. et al., The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/VIRGO GW170817. IV. Detection of Near-infrared Signatures of r-process Nucleosynthesis with Gemini-South, ApJL, arXiv:1710.05454
18. Coulter, D. A. et al., Swope Supernova Survey 2017a (SSS17a), the Optical Counterpart to a Gravitational Wave Source, Science, arXiv:1710.05452
19. Covino, S. et al., The unpolarized macronova associated with the gravitational wave event GW170817, Nature Astronomy, arXiv:1710.05849
20. Cowperthwaite, P. S. et al., The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/VIRGO GW170817. II. UV, Optical, and Near-IR Light Curves and Comparison to Kilonova Models, ApJL, arXiv:1710.05840
21. Creminelli, P.; & Vernizzi, F., Dark Energy after GW170817, na, arXiv:1710.05877
22. Di Valentino, E.; & Melchiorri, A., Cosmological constraints combining Planck with the recent gravitational-wave standard siren measurement of the Hubble constant, na, arXiv:1710.06370
23. Diaz, M.C. et al., Observations of the first electromagnetic counterpart to a gravitational wave source by the TOROS collaboration, ApJL, arXiv:1710.05844
24. Drout, M. R. et al., Light Curves of the Neutron Star Merger GW170817/SSS17a: Implications for R-Process Nucleosynthesis, Science, arXiv:1710.05443
25. Evans, P.A. et al., Swift and NuSTAR observations of GW170817: detection of a blue kilonova, Science, arXiv:1710.05437
26. Ezquiaga, J. M.; & Zumalacarregui, M., Dark Energy after GW170817, na, arXiv:1710.05901
27. Fargion, D.; Khlopov, M.; & Oliva, P., Could GRB170817A be really correlated to a NS-NS merging?, Research in Astron. Astrophys. , arXiv:1710.05909
28. Fermi-LAT Collaboration, Fermi-LAT observations of the LIGO/Virgo event GW170817, na, arXiv:1710.05450
29. Fong, W. et al., The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/VIRGO GW170817. VIII. A Comparison to Cosmological Short-duration Gamma-ray Bursts, ApJL, arXiv:1710.05438
30. Gall, C. et al., Lanthanides or dust in kilonovae: lessons learned from GW170817, ApJL, arXiv:1710.05863
31. Goldstein, A. et al., An Ordinary Short Gamma-Ray Burst with Extraordinary Implications: Fermi-GBM Detection of GRB 170817A, ApJL, arXiv:1710.05446
32. Gompertz, B. P. et al., The Diversity of Kilonova Emission in Short Gamma-Ray Bursts, ApJ, submitted, arXiv:1710.05442
33. Gottlieb, O. et al., A cocoon shock breakout as the origin of the ?-ray emission in GW170817, MNRAS, arXiv:1710.05896
34. Granot, J.; Guetta, D.; & Gill, R., Lessons from the short GRB170817A — the First Gravitational Wave Detection of a Binary Neutron Star Merger, na, arXiv:1710.06407
35. Granot, J. et al., Off-Axis Emission of Short GRB Jets from Double Neutron St.r Mergers and GRB 170817A, MNRAS, arXiv:1710.06421
36. Guidorzi, C. et al., Improved Constraints on H0 from a combined analysis of gravitational-wave and electromagnetic emission from GW170817, ApJL, submitted, arXiv:1710.06426
37. H.E.S.S. Collaboration et al., TeV gamma-ray observations of the binary neutron star merger GW170817 with H.E.S.S, ApJL, submitted, arXiv:1710.05862
38. Haggard, D. et al., A Deep Chandra X-ray Study of Neutron Star Coalescence GW170817, ApJL, arXiv:1710.05852
39. Hallinan, G. et al., A Radio Counterpart to a Neutron Star Merger, Science, arXiv:1710.05435
40. He, X.-B.; Tam, P-H. T.; & Shen, R. F.), GRB 170817A: a short GRB seen off-axis, MNRAS, arXiv:1710.05869
41. Hjorth, J. et al., The Distance to NGC 4993: The Host Galaxy of the Gravitational-wave Event GW170817, ApJL, arXiv:1710.05856
42. Hu, L. et al., Optical Observations of LIGO Source GW 170817 by the Antarctic Survey Telescopes at Dome A, Antarctica, Science Direct, arXiv:1710.05462
43. Im, M. et al., Distance and properties of NGC 4993 as the host galaxy of a gravitational wave source, GW170817, ApJL, arXiv:1710.05861
44. Ioka, K.; & Nakamura, T., Can an Off-axis Gamma-Ray Burst Jet in GW170817 Explain All the Electromagnetic Counterparts?, Prog. Theor. Exp. Phys. , arXiv:1710.05905
45. Kasen, D. et al., Origin of the heavy elements in binary neutron-star mergers from a gravitational wave event, Nature, arXiv:1710.05463
46. Kasliwal, M. M. et al., Illuminating Gravitational Waves: A Concordant Picture of Photons from a Neutron Star Merger, Science, arXiv:1710.05436
47. Kilpatrick, C. D. et al., Electromagnetic Evidence that SSS17a is the Result of a Binary Neutron Star Merger, Science, arXiv:1710.05434
48. Kim, S. et al., ALMA and GMRT constraints on the off-axis gamma-ray burst 170817A from the binary neutron star merger GW170817, na, arXiv:1710.05847
49. Lamb, G. P.; & Shiho Kobayashi, GRB 170817A as a jet counterpart to gravitational wave trigger GW 170817, MNRAS, arXiv:1710.05857
50. Levan, A. J. et al., The environment of the binary neutron star merger GW170817, ApJL, arXiv:1710.05444
51. Li, T.-P. et al., Insight-HXMT observations of the first binary neutron star merger GW170817, Sci. China-Phys. Mech. Astron. , arXiv:1710.06065
52. LIGO Scientific Collaboration, Virgo Collaboration, Fermi Gamma-Ray Burst Monitor, INTEGRAL, Gravitational Waves and Gamma-rays from a Binary Neutron Star Merger: GW170817 and GRB 170817A, ApJL, arXiv:1710.05834
53. LIGO Scientific Collaboration, Virgo Collaboration, et al., Multi-messenger Observations of a Binary Neutron Star Merger, ApJL, arXiv:1710.05833
54. Lipunov, V. M. et al., MASTER optical detection of the first LIGO/Virgo neutron stars merging GW170817, ApJL, arXiv:1710.05461
55. Lipunov, V. et al., Discovery of the neutron stars merger GW170817/GRB170817A and Binary Stellar Evolution, New Astronomy Review, arXiv:1710.05911
56. Lu, R.-J. et al., {\em Fermi}/GBM Short Gamma-ray Burst Catalog and Case Study for GRB 170817A/GW 170817, na, arXiv:1710.06979
57. Margalit, B.; & Metzger, B., Constraining the Maximum Mass of Neutron Stars From Multi-Messenger Observations of GW170817, ApJL, submitted, arXiv:1710.05938
58. Margutti, R. et al., The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/VIRGO GW170817. V. Rising X-ray Emission from an Off-Axis Jet, ApJL, arXiv:1710.05431
59. McCully, C. et al., The Rapid Reddening and Featureless Optical Spectra of the optical counterpart of GW170817, AT 2017gfo, During the First Four Days, ApJL, arXiv:1710.05853
60. Metzger, B. D. , Welcome to the Multi-Messenger Era! Lessons from a Neutron Star Merger and the Landscape Ahead, na, arXiv:1710.05931
61. Murguia-Berthier, A. et al., A Neutron Star Binary Merger Model for GW170817/GRB170817a/SSS17a, ApJL, arXiv:1710.05453
62. Nicholl, M. et al., The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/VIRGO GW170817. III. Optical and UV Spectra of a Blue Kilonova From Fast Polar Ejecta, ApJL, arXiv:1710.05456
63. Palmese, A. et al., DECam and DES perspective of the GW170817 host, NGC 4993: indication for dynamically-driven formation of binary neutron star in early type galaxies, na, arXiv:1710.06748
64. Pan, Y.-C. et al., The Old Host-Galaxy Environment of SSS17a, the First Electromagnetic Counterpart to a Gravitational Wave Source, ApJL, arXiv:1710.05439
65. Paul, D., Binary neutron star merger rate via the luminosity function of short gamma-ray bursts, MNRAS, arXiv:1710.05620
66. Pian, E. et al., Spectroscopic identification of r-process nucleosynthesis in a double neutron star merger, Nature, arXiv:1710.05858
67. Piro, A. L.; & Kollmeier, J. A., Evidence for Cocoon Emission from the Early Light Curve of SSS17a, na, arXiv:1710.05822
68. Pozanenko, A. et al., GRB170817A associated with GW170817: multifrequency observations and modeling of prompt gamma-ray emission, ApJL, submitted, arXiv:1710.05448
69. Rosswog, S. et al., The first direct double neutron star merger detection: implications for cosmic nucleosynthesis, A&A, accepted?, arXiv:1710.05445
70. Sakstein, J.; & Jain, B., Implications of the Neutron Star Merger GW170817 for Cosmological Scalar-Tensor Theories, na, arXiv:1710.05893
71. Salafia, O. S.; Ghisellini, G.; & Ghirlanda, G., Jet-driven and jet-less fireballs from compact binary mergers, MNRAS Letters, arXiv:1710.05859
72. Savchenko, V. et al., INTEGRAL Detection of the First Prompt Gamma-Ray Signal Coincident with the Gravitational Wave Event GW170817, ApJL, arXiv:1710.05449
73. Scolnic, D. et al., How Many Kilonovae Can Be Found in Past, Present, and Future Survey Datasets?, ApJL, submitted, arXiv:1710.05845
74. Seto, N.; & Kyutoku, K., Prospects of the local Hubble parameter measurement using gravitational waves from double neutron stars, MNRAS, arXiv:1710.06424
75. Shappee, B. J. et al., Early Spectra of the Gravitational Wave Source GW170817: Evolution of a Neutron Star Merger, Science, arXiv:1710.05432
76. Shoemaker, I. M.; & Murase, K., Constraints from the Time Lag between Gravitational Waves and Gamma Rays: Implications of GW 170817 and GRB 170817A, na, arXiv:1710.06427
77. Siebert, M. R. et al., The Unprecedented Properties of the First Electromagnetic Counterpart to a Gravitational Wave Source, ApJL, arXiv:1710.05440
78. Smartt, S. J. et al., A kilonova as the electromagnetic counterpart to a gravitational-wave source, Nature, arXiv:1710.05841
79. Soares-Santos, M. et al., The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. I. Dark Energy Camera Discovery of the Optical Counterpart, ApJL, arXiv:1710.05459
80. Tanaka, M. et al., Kilonova from post-merger ejecta as an optical and near-infrared counterpart of GW170817, PASJ, arXiv:1710.05850
81. Tanvir, N. R. et al., The Emergence of a Lanthanide-Rich Kilonova Following the Merger of Two Neutron Stars, na, arXiv:1710.05455
82. The LIGO Scientific Collaboration, The Virgo Collaboration, GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral, Phys. Rev. Lett., arXiv:1710.05832
83. The LIGO Scientific Collaboration, the Virgo Collaboration, Estimating the Contribution of Dynamical Ejecta in the Kilonova Associated with GW170817, ApJL, arXiv:1710.05836
84. The LIGO Scientific Collaboration, the Virgo Collaboration, On the Progenitor of Binary Neutron Star Merger GW170817, ApJL, arXiv:1710.05838
85. Tominaga, N. et al., Subaru Hyper Suprime-Cam Survey for An Optical Counterpart of GW170817, PASJ, submitted, arXiv:1710.05865
86. Troja, E. et al., The X-ray counterpart to the gravitational wave event GW 170817, Nature, arXiv:1710.05433
87. Utsumi, Y. et al., J-GEM observations of an electromagnetic counterpart to the neutron star merger GW170817, PASJ, arXiv:1710.05848
88. Valenti, S. et al., The discovery of the electromagnetic counterpart of GW170817: kilonova AT 2017gfo/DLT17ck, ApJL, arXiv:1710.05854
89. Verrecchia, F. et al., AGILE Observations of the Gravitational Wave Source GW 170817: Constraining Gamma-Ray Emission from a NS-NS Coalescence, ApJL, submitted, arXiv:1710.05460
90. Wang, F. Y.; & Zou, Y. C., Measuring peculiar velocities from gravitational waves and electromagnetic counterparts, na, arXiv:1710.06113
91. Wang, H. et al., GW170817/GRB 170817A/AT2017gfo association: some implications for physics and astrophysics, na, arXiv:1710.05805
92. Wei, J.-J. et al., Multimessenger tests of the weak equivalence principle from GW170817 and its electromagnetic counterparts, na, arXiv:1710.05860
93. Xiao, D. et al., Afterglows and Macronovae Associated with Nearby Low-Luminosity Short-Duration Gamma-Ray Bursts: Application to GW170817/GRB170817A, na, arXiv:1710.05910
94. Yang, S. et al., An empirical limit on the kilonova rate from the DLT40 one day cadence Supernova Survey, ApJL, submitted, arXiv:1710.05864
95. Yue, C. et al., Is GRB 170817A Alone?, na, arXiv:1710.05942
96. Zhang, B.-B. et al., A peculiar low-luminosity short gamma-ray burst from a double neutron star merger progenitor, na, arXiv:1710.05851

Rise Of The Super Telescopes: The Wide Field Infrared Survey Telescope

NASA's Wide Field Infrared Survey Telescope (WFIRST) will capture Hubble-quality images covering swaths of sky 100 times larger than Hubble does, enabling cosmic evolution studies. Its Coronagraph Instrument will directly image exoplanets and study their atmospheres. Credits: NASA/GSFC/Conceptual Image Lab

We humans have an insatiable hunger to understand the Universe. As Carl Sagan said, “Understanding is Ecstasy.” But to understand the Universe, we need better and better ways to observe it. And that means one thing: big, huge, enormous telescopes.

In this series we’ll look at the world’s upcoming Super Telescopes:

The Wide Field Infrared Survey Telescope (WFIRST)

It’s easy to forget the impact that the Hubble Space Telescope has had on our state of knowledge about the Universe. In fact, that might be the best measurement of its success: We take the Hubble, and all we’ve learned from it, for granted now. But other space telescopes are being developed, including the WFIRST, which will be much more powerful than the Hubble. How far will these telescopes extend our understanding of the Universe?

“WFIRST has the potential to open our eyes to the wonders of the universe, much the same way Hubble has.” – John Grunsfeld, NASA Science Mission Directorate

The WFIRST might be the true successor to the Hubble, even though the James Webb Space Telescope (JWST) is often touted as such. But it may be incorrect to even call WFIRST a telescope; it’s more accurate to call it an astrophysics observatory. That’s because one of its primary science objectives is to study Dark Energy, that rather mysterious force that drives the expansion of the Universe, and Dark Matter, the difficult-to-detect matter that slows that expansion.

WFIRST will have a 2.4 meter mirror, the same size as the Hubble. But, it will have a camera that will expand the power of that mirror. The Wide Field Instrument is a 288-megapixel multi-band near-infrared camera. Once it’s in operation, it will capture images that are every bit as sharp as those from Hubble. But there is one huge difference: The Wide Field Instrument will capture images that cover over 100 times the sky that Hubble does.

Alongside the Wide Field Instrument, WFIRST will have the Coronagraphic Instrument. The Coronagraphic Instrument will advance the study of exoplanets. It’ll use a system of filters and masks to block out the light from other stars, and hone in on planets orbiting those stars. This will allow very detailed study of the atmospheres of exoplanets, one of the main ways of determining habitability.

WFIRST is slated to be launched in 2025, although it’s too soon to have an exact date. But when it launches, the plan is for WFIRST to travel to the Sun-Earth LaGrange Point 2 (L2.) L2 is a gravitationally balanced point in space where WFIRST can do its work without interruption. The mission is set to last about 6 years.

Probing Dark Energy

“WFIRST has the potential to open our eyes to the wonders of the universe, much the same way Hubble has,” said John Grunsfeld, astronaut and associate administrator of NASA’s Science Mission Directorate at Headquarters in Washington. “This mission uniquely combines the ability to discover and characterize planets beyond our own solar system with the sensitivity and optics to look wide and deep into the universe in a quest to unravel the mysteries of dark energy and dark matter.”

In a nutshell, there are two proposals for what Dark Energy can be. The first is the cosmological constant, where Dark Energy is uniform throughout the cosmos. The second is what’s known as scalar fields, where the density of Dark Energy can vary in time and space.

We used to think that the Universe expanded at a steady rate. Then in the 1990s we discovered that the expansion had started accelerating about 5 billion years ago. Dark Energy is the name given to the force driving that expansion. Image: NASA/STSci/Ann Feild
We used to think that the Universe expanded at a steady rate. Then in the 1990s we discovered that the expansion had accelerated. Dark Energy is the name given to the force driving that expansion. Image: NASA/STSci/Ann Feild

Since the 1990s, observations have shown us that the expansion of the Universe is accelerating. That acceleration started about 5 billion years ago. We think that Dark Energy is responsible for that accelerated expansion. By providing such large, detailed images of the cosmos, WFIRST will let astronomers map expansion over time and over large areas. WFIRST will also precisely measure the shapes, positions and distances of millions of galaxies to track the distribution and growth of cosmic structures, including galaxy clusters and the Dark Matter accompanying them. The hope is that this will give us a next level of understanding when it comes to Dark Energy.

If that all sounds too complicated, look at it this way: We know the Universe is expanding, and we know that the expansion is accelerating. We want to know why it’s expanding, and how. We’ve given the name ‘Dark Energy’ to the force that’s driving that expansion, and now we want to know more about it.

Probing Exoplanets

Dark Energy and the expansion of the Universe is a huge mystery, and a question that drives cosmologists. (They really want to know how the Universe will end!) But for many of the rest of us, another question is even more compelling: Are we alone in the Universe?

There’ll be no quick answer to that one, but any answer we find begins with studying exoplanets, and that’s something that WFIRST will also excel at.

Artist's concept of the TRAPPIST-1 star system, an ultra-cool dwarf that has seven Earth-size planets orbiting it. We're going to keep finding more and more solar systemsl like this, but we need observatories like WFIRST, with starshades, to understand the planets better. Credits: NASA/JPL-Caltech
Artist’s concept of the TRAPPIST-1 star system, an ultra-cool dwarf that has seven Earth-size planets orbiting it. We’re going to keep finding more and more solar systems like this, but we need observatories like WFIRST to understand the planets better. Credits: NASA/JPL-Caltech

“WFIRST is designed to address science areas identified as top priorities by the astronomical community,” said Paul Hertz, director of NASA’s Astrophysics Division in Washington. “The Wide-Field Instrument will give the telescope the ability to capture a single image with the depth and quality of Hubble, but covering 100 times the area. The coronagraph will provide revolutionary science, capturing the faint, but direct images of distant gaseous worlds and super-Earths.”

“The coronagraph will provide revolutionary science, capturing the faint, but direct images of distant gaseous worlds and super-Earths.” – Paul Hertz, NASA Astrophysics Division

The difficulty in studying exoplanets is that they are all orbiting stars. Stars are so bright they make it impossible to see their planets in any detail. It’s like staring into a lighthouse miles away and trying to study an insect near the lighthouse.

The Coronagraphic Instrument on board WFIRST will excel at blocking out the light of distant stars. It does that with a system of mirrors and masks. This is what makes studying exoplanets possible. Only when the light from the star is dealt with, can the properties of exoplanets be examined.

This will allow detailed measurements of the chemical composition of an exoplanet’s atmosphere. By doing this over thousands of planets, we can begin to understand the formation of planets around different types of stars. There are some limitations to the Coronagraphic Instrument, though.

The Coronagraphic Instrument was kind of a late addition to WFIRST. Some of the other instrumentation on WFIRST isn’t optimized to work with it, so there are some restrictions to its operation. It will only be able to study gas giants, and so-called Super-Earths. These larger planets don’t require as much finesse to study, simply because of their size. Earth-like worlds will likely be beyond the power of the Coronagraphic Instrument.

These limitations are no big deal in the long run. The Coronagraph is actually more of a technology demonstration, and it doesn’t represent the end-game for exoplanet study. Whatever is learned from this instrument will help us in the future. There will be an eventual successor to WFIRST some day, perhaps decades from now, and by that time Coronagraph technology will have advanced a great deal. At that future time, direct snapshots of Earth-like exoplanets may well be possible.

But maybe we won’t have to wait that long.

Starshade To The Rescue?

There is a plan to boost the effectiveness of the Coronagraph on WFIRST that would allow it to image Earth-like planets. It’s called the EXO-S Starshade.

The EXO-S Starshade is a 34m diameter deployable shading system that will block starlight from impairing the function of WFIRST. It would actually be a separate craft, launched separately and sent on its way to rendezvous with WFIRST at L2. It would not be tethered, but would orient itself with WFIRST through a system of cameras and guide lights. In fact, part of the power of the Starshade is that it would be about 40,000 to 50,000 km away from WFIRST.

Dark Energy and Exoplanets are priorities for WFIRST, but there are always other discoveries awaiting better telescopes. It’s not possible to predict everything that we’ll learn from WFIRST. With images as detailed as Hubble’s, but 100 times larger, we’re in for some surprises.

“This mission will survey the universe to find the most interesting objects out there.” – Neil Gehrels, WFIRST Project Scientist

“In addition to its exciting capabilities for dark energy and exoplanets, WFIRST will provide a treasure trove of exquisite data for all astronomers,” said Neil Gehrels, WFIRST project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “This mission will survey the universe to find the most interesting objects out there.”

With all of the Super Telescopes coming on line in the next few years, we can expect some amazing discoveries. In 10 to 20 years time, our knowledge will have advanced considerably. What will we learn about Dark Matter and Dark Energy? What will we know about exoplanet populations?

Right now it seems like we’re just groping towards a better understanding of these things, but with WFIRST and the other Super Telescopes, we’re poised for more purposeful study.