UFO'S of UAP'S, ASTRONOMIE, RUIMTEVAART, ARCHEOLOGIE, OUDHEIDKUNDE, SF-SNUFJES EN ANDERE ESOTERISCHE WETENSCHAPPEN

"Instead, we have identified a population of pulsars in the region around the galactic center, which sheds new light on the formation history of the Milky Way," added Di Mauro, who led the analysis for the Fermi LAT Collaboration. This is a group of researchers who used the Large Area Telescope on NASA's Fermi Gamma-ray Space Telescope to study the galaxy's gamma-ray glow.

The sky in gamma-rays with energies greater than 1 gigaelectronvolts, based on eight years of data from the Large Area Telescope on NASA’s Fermi Gamma-ray Space Telescope. — **Credit: NASA/DOE/Fermi LAT Collaboration**

Hunting for dark matter

**Astronomers know more about what dark matter is not than what it actually is. See what scientists know about dark matter in this Space.com infographic.**
**Credit: Karl Tate, Space.com Infographics Artist**

Though dark matter apparently neither emits nor absorbs light (hence the name), astronomers know the stuff exists; they have observed its gravity affecting the "normal" matter we can see and touch. Indeed, such work suggests that dark matter makes up about 85 percent of the material universe.

However, scientists still don't know what the mysterious stuff is. One leading hypothesis holds that dark matter is composed mostly of Weakly Interacting Massive Particles (WIMPs). Theoretical physicists think that WIMPs generate gamma-rays when they interact with each other, either via direct annihilation or the production of a fast-decaying secondary particle.

So it was exciting when, several years ago, Fermi spotted an "excess" of gamma-rays near the Milky Way's core that astronomers said could not be explained by traditional sources such as pulsars. Process of elimination seemed to indicate that dark matter — in the form of WIMPs — was responsible.

The researchers behind such studies stressed at the time that this interpretation was tentative and in need of backing by other observations.

Pulsars the culprit?

Such confirmation has yet to materialize.

"Two recent studies by teams in the U.S. and the Netherlands have shown that the gamma-ray excess at the galactic center is speckled, not smooth as we would expect for a dark matter signal," KIPAC's Eric Charles, who contributed to the new analysis, said in the same statement.

"Those results suggest the speckles may be due to point sources that we can't see as individual sources with the LAT because the density of gamma-ray sources is very high and the diffuse glow is brightest at the galactic center," Charles added.

The new study further supports this idea, linking the speckled signal to pulsars.

"Considering that about 70 percent of all [gamma-ray] point sources in the Milky Way are pulsars, they were the most likely candidates," Di Mauro said. "But we used one of their physical properties to come to our conclusion. Pulsars have very distinct spectra — that is, their emissions vary in a specific way with the energy of the gamma-rays they emit. Using the shape of these spectra, we were able to model the glow of the galactic center correctly with a population of about 1,000 pulsars and without introducing processes that involve dark matter particles."

There are other reasons to doubt that the gamma-ray excess is being generated by dark matter, study team members said.

"If the signal were due to dark matter, we would expect to see it also at the centers of other galaxies," Seth Digel, head of KIPAC’s Fermi group, said in the same statement. "The signal should be particularly clear in dwarf galaxies orbiting the Milky Way. These galaxies have very few stars, typically don’t have pulsars and are held together because they have a lot of dark matter. However, we don't see any significant gamma-ray emissions from them."

The team plans to observe the Milky Way's center with radio telescopes, in an attempt to determine if the point sources there are emitting their light in pulses, as pulsars seem to do. (This is just an illusion, however. Pulsars emit light beams continuously in opposite directions; the light appears to flicker because pulsars spin, and their beams are therefore not always pointing at Earth.)

The new study has been submitted to The Astrophysical Journal. You can read it for free at the online preprint site arXiv.org.

Follow Mike Wall on Twitter @michaeldwall and Google+. Follow us @Spacedotcom, Facebook or Google+. Originally published on Space.com.

Gerstenmaier said, in response to one recommendation in the GAO report, that NASA would develop a new launch readiness date by the end of September. "NASA is assessing the EM-1 schedule in light of a number of ongoing activities," he said, which include the tornado that damaged the Michoud Assembly Facility in New Orleans in February, disrupting work on the core stage of the SLS, and the ongoing development of the administration's fiscal year 2018 budget request.

The GAO, in its examination of progress NASA was making on EM-1 requested by Congress in the report accompanying the fiscal year 2016 appropriations bill, had already concluded that the mission would not be ready for launch in late 2018 as planned. "With little to no schedule or cost reserves remaining as the programs finalize production and enter integration and testing activities, the EM-1 launch readiness date is in a precarious position," the report stated.

The GAO noted in the report progress made in the development of SLS, Orion and ground systems, but added that all faced serious challenges with little margin. "The magnitude of the schedule delays that the programs have experienced amid this progress, however, foreshadows a likely schedule slip for the November 2018 EM-1 launch readiness date," the report concluded.

One example is the delivery of the European-built service module for Orion, which is on the critical path for EM-1. Once scheduled for delivery in January, it has been delayed until at least August. Once delivered, the program requires 12 months of work to integrate it with the crew capsule and perform testing before delivering it to the Kennedy Space Center for final launch preparations.

"NASA officials stated that they would not be able to maintain a launch readiness date of November 2018 if Kennedy Space Center receives the Orion spacecraft after July 2018," the report noted. "As a result, the November 2018 launch readiness date is likely unachievable unless NASA identifies further mitigation steps to accommodate delays." The conclusion of the report added that the service module is now expected to be delivered in September, with the possibility of an additional two-month delay.

The report is the second in two weeks to conclude that delays in the SLS/Orion program were all but certain. An April 13 report by NASA's Office of Inspector General concluded that both EM-1 and EM-2, the first launch to carry a crew, faced schedule slips. "NASA's first exploration missions – EM-1 and EM-2 – face multiple technical challenges that will likely delay their launch," that report stated.

Delays in the EM-1 schedule don't take into account the possibility of placing a crew on that flight. NASA announced in February it was studying adding a crew to that mission. That report has been completed and briefed to both NASA Acting Administrator Robert Lightfoot and White House officials. The agency has not announced a decision, although one is expected by the time the White House releases its detailed fiscal year 2018 budget proposal, expected by mid-May.

One condition on that study, Gerstenmaier said in February, was that adding crew not delay EM-1 past the end of 2019. "I didn't want to go much beyond 2019," he said in a Feb. 24 briefing. "I felt that if we went much beyond 2019, then we might as well fly EM-2 and actually do the plan we're on."

That study had its origins in expected delays in EM-1. Chris Shank, who led the NASA transition team for the incoming Trump administration, said during a panel session at the Goddard Memorial Symposium March 8 that the study had its origins at a meeting where Gerstenmaier said the delivery of the Orion service module would likely be delayed.

"We asked, if given more time, if there are some additional things that you could do with the mission," he recalled. "This is genuinely a study on how to get the best bang for the buck."

This story was provided by SpaceNews, dedicated to covering all aspects of the space industry.