Scientists stunned by discovery of galaxy without dark matter
Most galaxies are defined by their dark matter. To study dark matter — and affirm its existence — astronomers studied galaxies.
Now, for the first time, scientists have found a galaxy without dark matter — NGC1052DF2’S dark matter is missing. When astronomers first found the dark matter-less galaxy, they were stunned, UPI wrote.
Pieter van Dokkum of Yale University in the US said, “For decades, we thought that galaxies start their lives as blobs of dark matter.
“After that everything else happens: Gas falls into the dark matter halos, the gas turns into stars, they slowly build up, and then you end up with galaxies like the Milky Way. NGC1052DF2 challenges the standard ideas of how we think galaxies form.”
The galaxy is an ultra-diffuse galaxy, it’s large and faint, and is located 65 million light-years away.
Though ultra-diffuse galaxies were only recently discovered, they are relatively common. But NGC1052-DF2 is the first to be found without dark matter.
Yale grad student Shany Danieli said, “NGC1052-DF2 is an oddity, even among this unusual class of galaxy.”
Astronomers were first alerted to the galaxy’s strange composition when they noticed discrepancies in the observations made by the Dragonfly Telephoto Array and the Sloan Digital Sky Survey (SDSS).
The Dragonfly images revealed a faint, blob-like object, while SDSS renderings showed a collection of bright point-like sources.
To further explore the discrepancy and study the unusual internal structure of NGC1052DF2, astronomers observed the galaxy using the Gemini Multi Object Spectrograph, Keck’s Deep Imaging Multi-object Spectrograph and Low-resolution Imaging Spectrometer.
Danieli added, “Without the Gemini images dissecting the galaxy’s morphology we would have lacked context for the rest of the data.
“Also, Gemini’s confirmation that NGC1052-DF2 is not currently interacting with another galaxy will help us answer questions about the conditions surrounding its birth.”
The Keck data showed the point-like sources, the globules, were moving much slower than astronomers expected.
The movement and speed of a galaxy’s components allow scientists to measure the galaxy’s mass.
Astronomers determined the galaxy’s stars accounted for all of NGC1052-DF2’S estimated mass. There was no dark matter to be found.
Researchers described their discovery in the journal Nature.
Van Dokkum said, “If there is any dark matter at all, it’s very little.
“The stars in the galaxy can account for all of the mass, and there doesn’t seem to be any room for dark matter.”
No one is really sure how the galaxy formed without dark matter.
The presence of the nearby giant elliptical galaxy NGC 1052, home to violent galactic formation and evolution, could explain NGC1052-DF2’S lack of dark matter.
It’s also possible a sudden burst of stellar formation swept away the galaxy’s gas and dark matter, stunting its development. As we generate more and more data, the need for high-density data storage that remains stable over time is becoming critical.
New nanoparticle-based films that are more than 80 times thinner than a human hair may help to fill this need by providing materials that can holographically archive more than 1,000 times more data than a DVD in a 10-by-10-centimeter piece of film, phys.org reported.
The new technology could one day enable tiny wearable devices that capture and store 3D images of objects or people.
Shencheng Fu, who led researchers from Northeast Normal University in China who developed the new films, said, “In the future, these new films could be incorporated into a tiny storage chip that records 3D color information that could later be viewed as a 3D hologram with realistic detail.
“Because the storage medium is environmentally stable, the device could be used outside or even brought into the harsh radiation conditions of outer space.”
In the journal Optical Materials Express, the researchers detail their fabrication of the new films and demonstrate the technology’s ability to be used for an environmentally-stable holographic storage system.
The films not only hold large amounts of data, but that data can also be retrieved at speeds up to 1 GB per second, which is about twenty times the reading speed of today’s flash memory.
Storing more data in less space
The new films are designed for holographic data storage, a technique that uses lasers to create and read a 3D holographic recreation of data in a material.
Because it can record and read millions of bits at once, holographic data storage is much faster than optical and magnetic approaches typically used for data storage today, which record and read individual bits one at a time.
Holographic approaches are also inherently high-density because they record information throughout the 3D volume of the material, not just on the surface, and can record multiple images in the same area using light at different angles or consisting of different colors.
Recently, researchers have been experimenting with using metal-semiconductor nanocomposites as a medium for storing nanoscale holograms with high spatial resolution.
Porous films made of the semiconductor titania and silver nanoparticles are promising for this application because they change color when exposed to various wavelengths, or colors, of laser light and because a set of 3D images can be recorded at the focus area of laser beam using a single step.
Although the films could be used for multiwavelength holographic data storage, exposure to UV light has been shown to erase the data, making the films unstable for long-term information storage.
Recording a holographic image into titania-silver films involves using a laser to convert the silver particles into silver cations, which have a positive charge due to extra electrons.
Fu said, “We noticed that UV light could erase the data because it caused electrons to transfer from the semiconductor film to the metal nanoparticles, inducing the same photo transformation as the laser.
“Introducing electron-accepting molecules into the system causes some of the electrons to flow from the semiconductor to these molecules, weakening the ability of UV light to erase the data and creating an environmentally stable high-density data storage medium.”
For the new films, the researchers used electron-accepting molecules that measured only one to two nanometers to disrupt the electron flow from the semiconductor to the metal nanoparticles.
They fabricated semiconductor films with a honeycomb nanopore structure that allowed the nanoparticles, electron-accepting molecules and the semiconductor to all interface with each other.
The ultrasmall size of the electron-accepting molecules allowed them to attach inside the pores without affecting the pore structure. The final films were just 620 nanometers thick.
The researchers tested their new films and found that holograms can be written into them efficiently and with high stability even in the presence of UV light.
The researchers also demonstrated that using the electronacceptors to change the electron flow formed multiple electron transferring paths, making the material respond faster to the laser light and greatly accelerating the speed of data writing.
Fu added, “Particles made from noble metals such as silver are typically viewed as a slow-response media for optical storage.
“We show that using a new electron transport flow improves the optical response speed of the particles while still maintaining the particle’s other advantages for information storage.”
The researchers plan to test the environmental stability of the new films by performing outdoor tests.
They also point out that reallife application of the films would require the development of high efficiency 3D image reconstruction techniques and methods for color presentation for displaying or reading the stored data.