From Hubble: “Cosmic lenses support finding on faster than expected expansion of the Universe”

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26 January 2017
Sherry Suyu
Max Planck Institute for Astrophysics
Garching, Germany
Tel: +49 89 30000 2015
Email: suyu@mpa-garching.mpg.de

Vivien Bonvin
Institute of Physics, Laboratory of Astrophysics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Observatory of Sauverny
Versoix, Switzerland
Tel: +41 22 3792420
Email: vivien.bonvin@epfl.ch

Frederic Courbin
Institute of Physics, Laboratory of Astrophysics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Observatory of Sauverny
Versoix, Switzerland
Tel: +41 22 3792418
Email: frederic.courbin@epfl.ch

Mathias Jäger
ESA/Hubble, Public Information Officer
Garching, Germany
Tel: +49 176 62397500
Email: hubble@eso.org

1
By using galaxies as giant gravitational lenses, an international group of astronomers using the NASA/ESA Hubble Space Telescope have made an independent measurement of how fast the Universe is expanding. The newly measured expansion rate for the local Universe is consistent with earlier findings. These are, however, in intriguing disagreement with measurements of the early Universe. This hints at a fundamental problem at the very heart of our understanding of the cosmos.

Studied lensed quasars of H0LiCOW collaboration
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This montage shows the five lensed quasars and the foreground galaxies studied by the H0LICOW collaboration. Using these objects astronomers were able to make an independent measurement of the Hubble constant. They calculated that the Universe is actually expanding faster than expected on the basis of our cosmological model. Credit: ESA/Hubble, NASA, Suyu et al.

Lensed quasar
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B1608+656 is among the five best lensed quasars discovered to date. The two foreground galaxies smeared the light of the more distant quasar’s host galaxy into bright arcs. Credit: ESA/Hubble, NASA, Suyu et al.

The Hubble constant — the rate at which the Universe is expanding — is one of the fundamental quantities describing our Universe. A group of astronomers from the H0LiCOW collaboration, led by Sherry Suyu (associated with the Max Planck Institute for Astrophysics in Germany, the ASIAA in Taiwan and the Technical University of Munich), used the NASA/ESA Hubble Space Telescope and other telescopes [1] in space and on the ground to observe five galaxies in order to arrive at an independent measurement of the Hubble constant [2].

The new measurement is completely independent of — but in excellent agreement with — other measurements of the Hubble constant in the local Universe that used Cepheid variable stars and supernovae as points of reference [heic1611].

However, the value measured by Suyu and her team, as well as those measured using Cepheids and supernovae, are different from the measurement made by the ESA Planck satellite.

ESA/Planck
ESA/Planck

But there is an important distinction — Planck measured the Hubble constant for the early Universe by observing the cosmic microwave background [CMB].

CMB per ESA/Planck
CMB per ESA/Planck

While the value for the Hubble constant determined by Planck fits with our current understanding of the cosmos, the values obtained by the different groups of astronomers for the local Universe are in disagreement with our accepted theoretical model of the Universe. “The expansion rate of the Universe is now starting to be measured in different ways with such high precision that actual discrepancies may possibly point towards new physics beyond our current knowledge of the Universe,” elaborates Suyu.

The targets of the study were massive galaxies positioned between Earth and very distant quasars — incredibly luminous galaxy cores. The light from the more distant quasars is bent around the huge masses of the galaxies as a result of strong gravitational lensing [3]. This creates multiple images of the background quasar, some smeared into extended arcs.

Because galaxies do not create perfectly spherical distortions in the fabric of space and the lensing galaxies and quasars are not perfectly aligned, the light from the different images of the background quasar follows paths which have slightly different lengths. Since the brightness of quasars changes over time, astronomers can see the different images flicker at different times, the delays between them depending on the lengths of the paths the light has taken. These delays are directly related to the value of the Hubble constant. “Our method is the most simple and direct way to measure the Hubble constant as it only uses geometry and General Relativity, no other assumptions,” explains co-lead Frédéric Courbin from EPFL, Switzerland

Using the accurate measurements of the time delays between the multiple images, as well as computer models, has allowed the team to determine the Hubble constant to an impressively high precision: 3.8% [4]. “An accurate measurement of the Hubble constant is one of the most sought-after prizes in cosmological research today,” highlights team member Vivien Bonvin, from EPFL, Switzerland. And Suyu adds: “The Hubble constant is crucial for modern astronomy as it can help to confirm or refute whether our picture of the Universe — composed of dark energy, dark matter and normal matter — is actually correct, or if we are missing something fundamental.”

Notes

[1] The study used, alongside the NASA/ESA Hubble Space Telescope, the Keck Telescope, ESO’s Very Large Telescope, the Subaru Telescope, the Gemini Telescope, the Victor M. Blanco Telescope, the Canada-France-Hawaii telescope [CFHT] and the NASA Spitzer Space Telescope. In addition, data from the Swiss 1.2-metre Leonhard Euler Telescope and the MPG/ESO 2.2-metre telescope were used.

Keck Observatory, Mauna Kea, Hawaii, USA
Keck Observatory, Mauna Kea, Hawaii, USA

ESO/VLT at Cerro Paranal, Chile, ESO/VLT at Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level
ESO/VLT at Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level.

NAOJ/Subaru Telescope at Mauna Kea Hawaii, USA
NAOJ/Subaru Telescope at Mauna Kea Hawaii, USA

Gemini/North telescope at Mauna Kea, Hawaii, USA
Gemini/North telescope at Mauna Kea, Hawaii, USA

NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile
NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile

CFHT Telescope, Mauna Kea, Hawaii, USA
CFHT Telescope, Mauna Kea, Hawaii, USA

NASA/Spitzer Telescope
NASA/Spitzer Telescope

ESO Swiss 1.2 meter  Leonhard Euler Telescope at La Silla
ESO Swiss 1.2 meter Leonhard Euler Telescope at La Silla

MPG/ESO 2.2 meter telescope at Cerro La Silla, Chile
MPG/ESO 2.2 meter telescope at Cerro La Silla, Chile

[2] The gravitational lensing time-delay method that the astronomers used here to achieve a value for the Hubble constant is especially important owing to its near-independence of the three components our Universe consists of: normal matter, dark matter and dark energy. Though not completely separate, the method is only weakly dependent on these.

[3] Gravitational lensing was first predicted by Albert Einstein more than a century ago. All matter in the Universe warps the space around itself, with larger masses producing a more pronounced effect. Around very massive objects, such as galaxies, light that passes close by follows this warped space, appearing to bend away from its original path by a clearly visible amount. This is known as strong gravitational lensing.

[4] The H0LiCOW team determined a value for the Hubble constant of 71.9±2.7 kilometres per second per Megaparsec. In 2016 scientists using Hubble measured a value of 73.24±1.74 kilometres per second per Megaparsec. In 2015, the ESA Planck Satellite measured the constant with the highest precision so far and obtained a value of 66.93±0.62 kilometres per second per Megaparsec.

This research was presented in a series of papers to appear in the Monthly Notices of the Royal Astronomical Society.

Link to science paper 1
Link to science paper 2
Link to science paper 3
Link to science paper 4
Link to science paper 5
H0LiCOW cooperation


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