The LISA Pathfinder Mission

by Eng. Andreea Monica Scorța

30.05.2025

Blog

The LISA Pathfinder mission was launched as a crucial step to demonstrate and validate the advanced technologies required for the upcoming LISA mission, which aims to detect gravitational waves by measuring incredibly tiny distortions in spacetime caused by massive celestial objects. To achieve this, LISA needs instruments capable of detecting changes as minuscule as the size of an atomic nucleus.

LISA Pathfinder served as a smaller-scale prototype of one arm of the full LISA observatory. It contained two free-floating test masses inside the spacecraft, whose relative positions were monitored with extreme precision using laser interferometry based on a heterodyne Mach-Zehnder setup. Capacitive sensors measured the displacement between the test masses, and this data was fed into a control system that adjusted micro-thrusters to keep the spacecraft perfectly cantered around the masses, effectively creating a drag-free environment.

LISA Pathfinder exploded view 

A key feature of LISA Pathfinder was its integrated spacecraft design, where the payload itself dictated the spacecraft’s attitude control, ensuring precise alignment. The mission carried two primary instruments: the LISA Technology Package (LTP), developed by European partners, which housed the test masses and acted as both mirrors for the interferometer and inertial references for the control system; and the Disturbance Reduction System (DRS), provided by ESA, which actively countered external forces such as solar radiation pressure that might disturb the spacecraft’s trajectory.

LISA Technology Package core assembly and inertial sensors

Launched on December 3, 2015, from French Guiana aboard a Vega rocket, LISA Pathfinder initially entered an elliptical parking orbit before using its propulsion system to travel to a stable halo orbit around the Sun-Earth Lagrange point L1, about 1.5 million kilometres from Earth. The mission officially began its science operations on March 1, 2016, with an initial planned duration of six months. However, due to its success, the mission was extended and continued gathering valuable data until June 30, 2017.

Overall, LISA Pathfinder’s achievements confirmed the feasibility of the drag-free technology and ultra-precise measurement techniques essential for the full LISA mission, paving the way for this future space-based gravitational wave observatory.

LISA Pathfinder's journey from launch to the L1 Sun-Earth Lagrangian point 

Source: https://www.esa.int/ESA_Multimedia/Images/2015/10/LISA_Pathfinder_s_journey

Neutrinos love complicated puzzles

by drd. Alice Mihaela Păun

23.05.2025

Neutrinos, also known as astrophysical messengers due to the vast distances they can travel through the Universe without interacting with matter, are extremely difficult to detect. For the detection of these particles, it was necessary to construct a neutrino telescope with a volume of 1 km³ and place it deep within the ice at the South Pole - the IceCube Neutrino Observatory [https://icecube.wisc.edu/]. Neutrinos that interact near the detector produce relativistic particles that generate luminous events, which can be "seen" by the "eyes" of the instrumentation (optical modules).

The data collected by IceCube concerning the galaxy NGC 1086 [1], also known as the Squid Galaxy, indicate a flux of very high-energy neutrinos (TeV), accompanied by an extremely weak flux of gamma rays (GeV) observed by the Fermi [2] and MAGIC [3] telescopes. NGC 1086 is an active galaxy with a central region (AGN – Active Galactic Nucleus) that contains a supermassive black hole and emits matter and energy in the form of jets. The discrepancy between the two particle fluxes represents an intriguing puzzle for researchers, because such active galactic nuclei typically emit neutrino and gamma-ray fluxes of comparable energies, resulting from interactions between protons and photons [4].

A recent article [5] offers a bold explanation for the neutrino puzzle observed from AGNs, which aligns with current observations: a new mechanism for producing high-energy neutrinos.
The source of the neutrino flux could be the corona — a region of dense, hot plasma surrounding the central supermassive black hole. The most abundant elements in the Universe are hydrogen and helium. Therefore, if a helium nucleus is accelerated in the jets of a supermassive black hole, it can collide with ultraviolet photons and "break apart", releasing its two protons and two neutrons [4]. Protons have a long lifetime, but neutrons are unstable and decay into high-energy neutrinos without producing gamma rays. The electrons generated in the decay interact with radiation fields and produce gamma rays that match the observed data.

The results of this study help us better understand how matter jets in active galaxies work and how high-energy neutrinos can be produced without a corresponding flux of gamma rays.

Galaxia Messier 77

Sursa foto: ESA/Hubble & NASA, L. C. Ho, D. Thilker

New Gravitational Waves Detector Configurations Were Discovered with the Help of Artificial Intelligence

by Maria Ișfan, PhD student

16.05.2025

Photo: https://humansofligo.blogspot.com/, https://news.mit.edu/

    LIGO is a gravitational waves detector which operates according to the Michelson laser interferometry principle. The detector configuration is typical. It involves two perpendicular laser beams, along with optical elements such as mirrors and beam splitters.

    Using only one laser beam, ten mirrors and beam splitters and two sensors, over one hundred million detector configurations can be obtained. With the help of the Urania artificial intelligence software, the researchers found fifty configurations which are better than the original one.

    Compared to LIGO, these potential new detectors show increased sensitivity, have lower noise levels and are able to better observe the post-coalescence signal emitted by two neutron stars.

    This new approach can be used for designing experiments in all areas of Physics, accelerating new scientific discoveries.

News source: https://journals.aps.org/prx/pdf/10.1103/PhysRevX.15.021012

Ancient footsteps in space-time

by Florentina Pîslan, PhD student

09.05.2025

    Currently, we know gravitational waves can be divided into four distinct categories based on their sources, detection methods, and frequencies: stochastic, continuous, inspiral, and burst. When two black holes collide, they create inspiral gravitational waves that not only propagate through the Universe, but also leave a permanent imprint on the space-time continuum - much like how a chair leaves an indentation in a carpet. This phenomenon is called the 'memory effect,' which could hold the key to discovering small, ancient black holes potentially formed in the early Universe, known as Primordial Black Holes (PBHs).

    Why are these objects so fascinating? Because they might be fragments from the Big Bang (even older than stars!) - as small as a city, yet as dense as a planet, and possibly the leading candidates for dark matter.

    In the paper 'Gravitational Wave Memory of Primordial Black Hole Mergers’ , researchers investigate whether future gravitational wave observatories like LISA and the Einstein Telescope could detect these objects. The detectors will aim to identify them both through the characteristic 'chirp' signal produced during collision and by analyzing their space-time imprint. To better understand the difference: the 'chirp' resembles an explosive but transient sound, while the memory effect is more like a permanent scar. Generally, the more massive the objects producing the 'chirp,' the easier the signal is to detect.

    The study reveals that due to the tiny size of Primordial Black Holes, the memory effect might be their only detectable signature. Observing this effect could provide groundbreaking confirmation of Einstein's predictions in entirely new ways.